This brussels sprouts and mushroom casserole topped with french fried onions is a twist on the Thanksgiving staple you have to try!

scooping brussels sprout and mushroom casserole out of baking dish

When it comes to Thanksgiving side dishes, how do you choose what to serve? Do you stick to the same handful of recipes year after year, or do you like to mix it up and try new ones? Do you go with more traditional side dishes, or do you branch out?

If you’re looking to shake up the norm this Thanksgiving, I highly recommend this recipe! This brussels sprouts and mushroom casserole is a fun variation on traditional green bean casserole, and honestly I love it so much more. It’s made completely from-scratch and has a creamy sauce filled with brussels sprouts and mushrooms, and finished with a crispy french onion topping. It’s cozy, savory, and very delicious.

ingredients for brussels sprout and mushroom casserole

Ingredients You’ll Need

  • Brussels sprouts
  • Cremini or baby bella mushrooms
  • Onion
  • Garlic
  • Butter
  • All-purpose flour
  • Chicken or vegetable broth
  • Half and half
  • Panko breadcrumbs
  • French fried onions
  • Salt and pepper

sautéed mushrooms and brussels sprouts

How to Make this Brussels Sprouts and Mushroom Casserole

1. Sauté brussels sprouts. Brown brussels sprouts in butter for several minutes until slightly caramelized, about 3-4 minutes. Transfer to a bowl and set aside.

2. Sauté mushrooms and onions. Add more butter, mushrooms and onions to the pan and cook for 3-4 minutes until soft. Add garlic and cook for 1 minute more. Add to bowl with brussels sprouts.

3. Make cream sauce. Add more butter and flour to the pan and whisk until smooth. Slowly add broth and then the half and half while whisking to make a smooth sauce. Simmer for a few minutes until thickened. Season to taste.

mushrooms and brussels sprouts in white sauce and adding topping in baking dish

4. Layer in casserole dish with topping. Combine cream sauce with brussels sprouts and mushrooms and dump into a greased casserole dish. Combine french fried onions and panko breadcrums and sprinkle over the top.

5. Bake. Bake at 375°F until bubbly and toppings is browned.

6. Serve. Let this casserole dish for a few minutes before serving. If you’d like to make this recipe ahead of time, see below!

brussels sprout and mushroom casserole out of the oven

Can this Dish be Made Ahead?

Absolutely! Fully bake this casserole, let cool to room temperature, and then store in the fridge up to 2 days ahead. To reheat, cover with foil and warm in a 350°F oven for about 30 minutes. Remove foil for the last 5-10 minute to get the topping nice and crispy again.

You can also make cooking easier the day of by prepping the vegetables ahead of time. Chop brussels sprouts, mushrooms, and onion up to 1 week in advance and store in the fridge until ready to use.

brussels sprout and mushroom casserole on plate

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This recipe was originally published November 2016.

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Brussels Sprouts and Mushroom Casserole

Servings: 8 servings
Prep Time: 20 mins
Cook Time: 20 mins
Total Time: 40 mins
This brussels sprouts and mushroom casserole topped with french fried onions is a twist on the Thanksgiving staple and one you have to try!
scooping brussels sprout and mushroom casserole out of baking dish
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4.50 from 4 votes

Ingredients

  • 8 tablespoons butter , divided
  • 1 ½ lb brussels sprouts , halved
  • 8 oz cremini or baby bella mushrooms , halved or quartered
  • ½ onion , chopped
  • 2 cloves of garlic , minced
  • 2 tablespoons all-purpose flour
  • 1 cup chicken or vegetable broth
  • 1 cup half and half
  • 1 cup panko breadcrumbs
  • 6 oz can of French fried onions
  • Salt and pepper , to taste

Instructions

  • Preheat oven to 375°F. Grease a 9x13 inch casserole dish with butter or nonstick spray.
  • Melt 2 tablespoons of butter in a large skillet set over medium heat. Add brussels sprouts and cook until browned, about 5 minutes. Transfer to a separate bowl and set aside.
  • Add another 2 tablespoons of butter, mushrooms and onions to the skillet, season with salt and pepper, and cook until soft, about 5-6 minutes. Add garlic and cook for 1 minute more. Add to the bowl with the brussels sprouts.
  • Melt 2 tablespoons of butter in skillet. Add flour and whisk to form a thick paste. Add chicken or vegetable broth gradually while whisking constantly. Whisk in half and half. Increase heat to medium high and bring to a boil, whisking frequently. Simmer until thick for about 5 minutes until thickened. Season with salt and pepper to taste.
  • Combine brussels sprouts mixture with the sauce and pour into the prepared casserole dish. Melt remaining 2 tablespoons of butter and combine with the breadcrumbs in a medium bowl. Add the french fried onions. Scatter mixture on top of the brussels sprouts mixture.
  • Bake casserole until bubbly and topping is brown, about 20-25 minutes.
Note: This casserole can be prepared ahead of time. Let baked casserole cool completely, then cover with plastic wrap and chill in the fridge for up to 2 days. To reheat, cover with foil and warm in a 350°F oven for about 30 minutes. Remove foil for the last 5-10 minute to get the topping nice and crispy again.

Nutrition

Calories: 356kcal, Carbohydrates: 27g, Protein: 6g, Fat: 26g, Saturated Fat: 14g, Cholesterol: 41mg, Sodium: 485mg, Potassium: 522mg, Fiber: 4g, Sugar: 3g, Vitamin A: 1161IU, Vitamin C: 73mg, Calcium: 91mg, Iron: 2mg
Course: Side Dish
Cuisine: American
Author: Annalise
Have you tried this recipe?I’d love to hear about it! Leave a review below or take a photo and tag it on Instagram @completelydelicious with #completelydelicious.