Creamy Butternut Squash and Spinach Casserole

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squash and spinach casserole cut into pieces

Creamy Butternut Squash and Spinach Casserole has just enough cream sauce between its layers to feel rich and festive. It’s a colorful vegetarian and gluten-free side dish that is perfect for the holidays.

I’ve been making a variation of this holiday side dish for as long as I can remember – sometimes at Thanksgiving and sometimes at Christmas. I was a vegetarian for many years and this beautiful layered casserole always felt special enough to be the main event for a vegetarian at the holidays. I’d alternate it with this beautiful and delicious Stuffed Butternut Squash.

If you’re not a fan of sweet potato casserole at the holiday or are looking for another colorful vegetable side dish, this is a great alternative.

sliced squash

Once the squash is sliced into thin disks (it’s worth pulling out a mandolin or using the shredding disk on your food processor for this), the rest is easy to make. And it can be completely assembled up to 3 days ahead to just bake whenever you’re ready. Here’s how to make it!

Ingredients

  • Butternut Squash – The key to the even, tender layers in the casserole is thinly sliced squash. If you have a mandolin, it’s worth getting it out to make quick and even work of slicing the squash. You can also use the shredding disk on a food processor. I only use my mandolin about twice a year and this is always one of my favorite ways to use it. 
  • Spinach – This works either with fresh or frozen spinach. If using frozen spinach, it can retain a lot of liquid, so defrost it first and squeeze as much moisture out as possible. Getting water out of the spinach is the key to a creamy (not watery) sauce.
  • Onions and Garlic – These aromatics add to the richness of the dish. Be sure to chop them very fine so they just melt right into the sauce.
  • Unsalted Butter – If using salted butter, be sure to reduce the additional salt you add. 
  • Heavy or Whipping Cream – Either heavy or whipping cream works to make the rich, creamy sauce. 
  • Parmesan Cheese – You’ll get the most smooth results if you grate this yourself, but pre-grated sauce will work.
  • Salt, Pepper, Ground Nutmeg – Use these to season the dish.

adding wet ingredients to dry in a skillet

How to Make Creamy Butternut Squash and Spinach Casserole Ahead

To prepare: Prepare the dish through the end of step 6, topping the casserole with parmesan and butter. Cover tightly with foil. Refrigerate for up to 3 days or freeze for up to 2 months.

To bake: To bake the dish, take it out of the fridge an hour before baking so that it comes to room temperature (if frozen, let it thaw in the fridge until fully defrosted). Bake as directed. 

adding fillings to the squash layer

oncooked casserole in a white baking dish

Possible Variations

  • Make it with different vegetables – This dish would be delicious made with thinly sliced sweet potatoes or Yukon gold potatoes in place of the butternut squash. 
  • Make it dairy-free – While not as rich, this dish is great when made with stock instead of cream. Or use a non-dairy milk alternative instead of cream. Saute the onions in olive oil and skip the parmesan. 
  • Bake it in ramekins – This is fun to bake in individual servings using ramekins or other small baking dishes. 

My Complete Thanksgiving Menu

Get more details and a complete Thanksgiving timeline here.

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squash and spinach casserole cut into pieces
4.89 from 17 votes

Creamy Butternut Squash and Spinach Casserole

Creamy Butternut Squash and Spinach Casserole has just enough cream sauce between its layers to feel rich and festive. It’s a colorful vegetarian and gluten-free side dish that is perfect for the holidays.
Prep: 45 minutes
Cook: 1 hour 15 minutes
Total: 1 hour 15 minutes
Servings: 12

Equipment

  • Saute Pan
  • 2 qt Casserole Dish or 9" Cake Pan

Ingredients 

  • 1 cup finely diced White Onion
  • 6 Tbsp Unsalted Butter, divided
  • 4 cloves Garlic, finely chopped
  • 1 tsp Kosher Salt
  • 1/2 tsp Black Pepper
  • 1/4 tsp Ground Nutmeg (preferably freshly grated)
  • 8 oz Baby Spinach, roughly chopped
  • 1 cup Heavy / Whipping Cream
  • 1 cup grated Parmesan Cheese, plus extra for topping
  • 1 3 lb Butternut Squash, peeled, seeds removed, and sliced into 1/8-inch slices

Instructions 

  • Preheat oven to 350°F / 177°C. Spray a 2-quart casserole dish (or use a 9-inch pie plate or 9-inch cake pan) with nonstick cooking spray or brush with some oil.
  • In a large saute pan over medium heat, melt 4 Tablespoons butter. Add onion and garlic and saute until onion is very soft, 7 to 8 minutes.
  • To onion mixture, add salt, black pepper, nutmeg, and baby spinach. Saute until spinach is wilted (put the lid on to speed it along) and all of the liquid has cooked off, 7 to 8 minutes.
  • Remove spinach from heat and whisk in heavy cream, parmesan cheese, and nutmeg.
  • Layer squash and spinach-cream mixture, using about one fifth of squash and one fourth of spinach for each layer, beginning and ending with squash.
  • Scatter parmesan cheese over top of casserole and dot with pieces of the remaining 2 Tablespoons of butter.
  • If using a baking dish with shallow sides (like a pie plate) place it on a sheet pan to catch any liquid that bubbles over).
  • Cover baking dish tightly with foil and bake until squash is nearly tender, 50 minutes. (Note: If the dish was made ahead and is cold when you transfer it to the oven, add 30 minutes to the initial baking time.)
  • Remove foil and continue baking until casserole is golden brown on top and bubbling around the sides, about 15 minutes more.

Notes

Butternut Squash - If you have a mandolin or the shredding attachment for a food processor, use it to make quick and even work of slicing the squash. This casserole is also great with sweet potatoes, Yukon gold potatoes, or a combination of any of those. 
Spinach - Frozen spinach can be used in place of fresh. Defrost the spinach and thoroughly squeeze out any moisture before adding it to the onions and garlic.
Make Ahead - Assemble the casserole up to 3 days ahead. Allow to come to room temperature before baking. 
Recipe inspired by Butternut Squash and Creamed-Spinach Gratin, Gourmet Magazine, November 2006.  

Nutrition

Calories: 166kcal | Carbohydrates: 3g | Protein: 4g | Fat: 16g | Saturated Fat: 10g | Cholesterol: 50mg | Sodium: 345mg | Potassium: 154mg | Fiber: 1g | Sugar: 1g | Vitamin A: 2320IU | Vitamin C: 7mg | Calcium: 131mg | Iron: 1mg

Nutrition information is automatically calculated, so should only be used as an approximation.

Author: Jess Smith via Inquiring Chef
Cost: $6.00
Calories: 166
Keyword: casserole, squash, Thanksgiving, vegetable side dish
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About Jess Smith

Jess is the recipe creator and photographer at InquiringChef.com. She spent nearly a decade as the Chief Recipe Developer for the award-winning meal planning app Cook Smarts. Her colorful, healthyish recipes have been featured in popular online publications including Parade, Hallmark, and HuffPost.

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8 Comments

    1. I haven’t made Thai squash soup, but it sounds like something I would definitely love! Do you happen to have a recipe you would be willing to share?

  1. wOW…LOOKS AMAZING! Great pics girlie! Don’t feel bad, I have 3 recipes from Summer I somehow have been keeping to myself… Not enough tie in the day! Esp. now when surgery is on Tuesday…boooooooooooooo.

    xoxo from Texas

    1. Oh no – surgery is scheduled?! I’m behind since I’ve been traveling. I’ll be thinking about you Tuesday – what a doozy of a year you’ve had friend.