Creamy Butternut Squash Gratin with Caramelized Onions

Elevate a fall favorite with this Creamy Butternut Squash Gratin with Caramelized Onions. This delightful side dish has scalloped butternut squash baked in a delicious creamy sauce made with golden onions, garlic, and thyme.

❤Why you'll love this gratin recipe

• Taste & Texture: This gratin qualifies as a comfort food with all those familiar tastes and homey textures of a potato au gratin but with a nutrient punch.
• Simple ingredients: It only calls for 5 basic ingredients yet comes with maximum flavor!
• Easy way to impress: Add this elegant side dish to your Thanksgiving table.

🍲Ingredients

This Creamy Butternut Squash Gratin with Caramelized Onions takes your favorite fall vegetable and combines it with all the classic gratin ingredients for an elevated version.

• butternut squash: any tomatoes will work but the best are those fresh from your garden or farmer's market
• onion: one yellow onion is all that is needed - go with large or medium onion
• fresh garlic: very important for pungent flavor
• fresh thyme: same as garlic - fresh is best but if not possible, go with dried thyme
• arrowroot flour or regular flour: to thicken the onions to make a cream sauce
• half and half: this creates a nice balance between the rich creaminess and watery liquid in the squash but you can use all heavy cream instead. Straight milk is not recommended as it will be too watery.

See recipe card for exact quantities.

💭Make it Nutrient-Dense: To bump up the nutrient content, use raw cream and top with raw cheddar for extra enzymes.

📖Substitutions and Variations

• Dairy Free - make this dairy free by using extra virgin olive oil instead of butter and coconut milk instead of half and half
• Fancy - use sage leaves instead of thyme and add gruyère cheese and toasted pancetta to take level up this gratin dish
• Deluxe - add more hominess by adding bacon bits, parmesan cheese, fresh bread crumbs, and red pepper flakes.

🌡️Caramelizing Onions

To truly maximize the flavors of this butternut squash recipe, caramelizing onions is important.

But I get it, it can also be a time consuming endeavor that is seemingly unnecessary. So if short on time, cook the onions just until translucent and softened. Alternatively, you can caramelize the onions well in advance up to 3 days of making the dish.

Caramelizing onions takes time as you are slowly coaxing the flavor out of them and turning the sugars into caramel type flavor and appearance.

Don't take them off too early - they should yield a rich brown, soft but not mushy onions. This usually takes 20-30 minutes.

Towards the end, more flavors are added and then thickened with arrowroot flour. Followed by a nice dose of cream -- this creates lush, decadent creamy mixture that will envelope the squash slices.

💭Helpful Tips

• 🕐Time Saving Tip: slice the butternut squash and make the caramelized onions up to 3 days in advance.
• 💲 Money Saving Tip: butternut squash has a long shelf life so stock up on this favorite fall vegetable now to make this dish well into spring.
• 🗓Make-Ahead Tip: you can prepare the dish with the creamy onion sauce and keep it covered in the refrigerator for up to 24 hours. Bring to room temperature before baking.
• 🚫Bake time: don't over bake the squash! You want it tender yet not mushy. Watch it and keep checking it at 30 minutes, as all ovens vary.

👩🏽‍🍳Step-by-Step Instructions

The complete printable recipe is below in the recipe card for your convenience.

This butternut squash gratin recipe calls for these ingredients: butternut squash, butter, yellow onion, fresh garlic, fresh thyme, arrowroot flour, half and half, and black pepper.

Step 1. Caramelize onions

Melt butter in a large skillet over medium heat. Add sliced onions and season with salt to release juices. Cook until onions are golden brown (approximately 25 minutes), stirring occasionally.

Step 2. Thicken onions

Add garlic, thyme (fresh or dried), and season with salt and pepper. Reduce heat to low-medium and add arrowroot starch (or flour) and quickly coat onion mixture with the flour.

💭Pro tip: Arrowroot flour and tapioca starch can be used interchangeably to thicken sauces. It is a great gluten free alternative to all purpose flour in this capacity.

Step 3. Add cream

Add half & half and whisk to combine everything, keeping heat at low-medium. Cook and whisk occasionally for approximately 5 minutes. Sauce should slightly thicken. 

Step 4. Prepare squash

Peel butternut squash with a vegetable peeler. Cut lengthwise with a sharp knife and remove seeds and pith. Thinly slice crosswise creating half moons. Make the slices approximately ⅛" thickness.

💭Pro tip: You may sub half and half with heavy whipping cream to create a very creamy sauce but I would not use regular milk as that would make the gratin very watery.

Step 5. Assemble gratin

Spoon ⅓ of the onion cream mixture to the bottom of the casserole dish. Arrange butternut squash slices across the dish in several layers.

Step 6. Top with creamy mixture

Spread remaining onion cream mixture evenly on top of the squash, creating pockets between the pan sides and slices to allow the infused cream to seep through.

Step 7. Bake gratin

Bake uncovered for 40 minutes on the middle rack. Broil for the last 5 minutes of cooking time to brown the tops but keep a close eye as oven temperature vary.

Remove from oven and allow to rest for 5 minutes for sauce to settle before serving. Garnish with fresh parsley if desired.

🔪Helpful Tools & Links

Below are some affiliate links that may be helpful to you as you make this recipe. You can find some of these items cheaper at your local store but it helps to have a link so you know what you're looking for.

• Tools: chef knife, cutting board, vegetable peeler, stainless steel frying pan, baking dish
• Ingredients: dried thyme, real salt, black pepper, olive oil, arrowroot flour
• Storage Supplies: glass snap containers

🥗Serving Suggestions

This elegant Creamy Butternut Squash Gratin can be served as a wonderful side dish with any main entree since those caramelized onions add lots of flavor. It pairs well with your Thanksgiving turkey or pork tenderloin for a weeknight dinner.

A nice way to round off this complete meal is to add a nice hearty salad like this Harvest Kale Salad or Caesar Salad with homemade Caesar Salad dressing and air fryer croutons.

♨️Storage and Reheating Instructions

To store: Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.

Storage containers: These glass snap containers are perfect for leftovers.

To reheat: The best way to reheat leftovers with some liquid is to transfer to a medium saucepan with lid, cover and gently reheat over medium-low heat until fully warmed through.

💬FAQs

Looking for more side dishes? Here are some ideas:

Did you make this? Please leave a ⭐ recipe rating in the recipe card below and leave a review in the comments. Thank you!💚

Printable Recipe

Creamy Butternut Squash Gratin with Caramelized Onions

Anya @ Prepare & Nourish

Thinly sliced butternut squash is enveloped in a thick creamy sauce of caramelized onions, garlic, and thyme.

4 from 3 votes

Print Recipe Pin Recipe Save RecipeSaved!

Prep Time 20 minutes mins

Cook Time 1 hour hr

Resting Time 5 minutes mins

Total Time 1 hour hr 25 minutes mins

Course Side Dish

Cuisine American

Servings 8 servings

Calories 263 kcal

Equipment

• vegetable peeler
• stainless steel frying pan
• oval stoneware casserole dish

Ingredients

  

1x2x3x

• 4 tablespoons butter
• 1 large onion sliced
• 4 garlic cloves
• 2 tablespoons fresh thyme
• 2 teaspoons sea salt
• ½ teaspoon black pepper
• 1 ½ tablespoons arrowroot flour
• 2 cups half and half
• 1 small butternut squash

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Instructions

 

• Preheat oven to 375 degrees Fahrenheit.

Caramelized Onion Cream Sauce

• Melt butter in a large skillet over medium heat. Add sliced onions and season with salt to release juices. Cook until onions are golden brown (approximately 25 minutes), stirring occasionally.
  
• Add garlic, thyme (fresh or dried), and season with salt and pepper. Reduce heat to low-medium and add arrowroot starch (or flour) and quickly coat onion mixture with the flour.
  
• Add half & half and whisk to combine everything, keeping heat at low-medium. Cook and whisk occasionally for approximately 5 minutes. Sauce should slightly thicken. 
  

Preparing Butternut Squash

• Peel butternut squash and cut lengthwise. Remove seeds and pith. Thinly slice crosswise creating half moons.
  

Assembling Butternut Squash Gratin

• Spoon ⅓ of the onion cream mixture to the bottom of the casserole dish. Arrange butternut squash slices across the dish in several layers.
  
• Pour remaining onion cream mixture, creating pockets between the pan sides and slices to allow the sauce to drip through. 
  
• Bake uncovered for 40 minutes on the middle rack. Broil for the last 5 minutes of cooking time to brown the tops. Remove from oven and allow to rest for 5 minutes for sauce to settle before serving.
  

Video

Notes

• Two tablespoons of fresh thyme is approximately 3-4 sprigs of thyme. Alternatively, you can use 2 teaspoons of dried thyme.
• Arrowroot flour is used to thicken the cream sauce. Tapioca can be used as well. If not gluten free, any all purpose flour can be used.
• To catch possible overflow of the creamy sauce, set a baking sheet with lip on the bottom rack during cooking.

Nutrition

Calories: 263kcal | Carbohydrates: 12g | Protein: 1g | Fat: 23g | Saturated Fat: 13g | Cholesterol: 74mg | Sodium: 516mg | Potassium: 320mg | Fiber: 1g | Sugar: 2g | Vitamin A: 8795IU | Vitamin C: 17.9mg | Calcium: 74mg | Iron: 0.6mg

Nutrition Information

The information shown is an estimate provided for your convenience by an online calculator. It should not be considered as a substitute for a professional nutritionist's advice. See our complete Nutritional Information Disclaimer.

Keyword butternut squash, butternut squash gratin

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This post was originally published November 2017 but has since been updated to include helpful information.