Oh boy! This Cheesy Spinach Mushroom and Onion Casserole is one that will certainly become a staple in your home! It's an incredibly versatile recipe that makes it easy to swap out types of cheese, leave out mushrooms or onions, add in meat or potatoes, etc. The choice is yours.
I first started making this Cheesy Spinach Mushroom Casserole when the boys were little. I was always trying to hide vegetables in my recipes and therefore trick the boys into eating healthy. It worked!
How do I know? One of my boys is now a Vegetarian, lol. They all love food and enjoy trying new ingredients and preparations. My twins, who are 27, both love to cook and will jump into the kitchen whenever they can.
This recipe is easy. I wrote this recipe using cheddar cheese only because my youngest child is currently living under our roof and cheddar is his favorite cheese. Covid-19 and the pandemic have sent him home from his senior year at college. I truly didn't think we would ever see any of our kids living at home but here we go. And Jordan is our vegetarian so my cooking has changed ever so slightly. If you would prefer a different type of cheese, feel free to swap it out. I also love a combination of mozzarella and parmesan. I have also used feta, which is delicious, but you will need to decrease the amount you use to cut down on the saltiness.
How to make Cheesy Spinach Mushroom Casserole
The first step to creating this masterpiece is to saute the mushrooms and onion in butter or olive oil, your choice. I use butter. I also used shitake mushrooms that I had on hand. You don't need to do that. I only had shitake in my fridge!
Cook your frozen spinach for about 4 minutes in the microwave which is enough to warm it up so you can squeeze the water out of it. But, in the picture above, I used cut spinach instead of chopped spinach. Chopped spinach works even better. I just didn't have it in my freezer!
Combine all of the ingredients and bake for about 45 minutes. You want the top to be lightly browned and the cheese to be gooey!
Cheesy Spinach Mushroom Casserole
- 2 oz frozen spinach 10 oz bag
- 1 whole onion chopped
- 5 oz mushrooms chopped
- 2 tablespoon butter
- 2 whole eggs
- 2 cups shredded cheese of choice
- 1 t salt
- ½ t pepper
- 2 t garlic powder
- Preheat the oven to 375 degrees. Grease a 9x13 casserole dish and set aside. Saute the onions in the butter until soft over medium heat. Add the mushrooms and saute until the mushrooms are just starting to brown. Turn off the heat and set aside. Cook the spinach and then drain the water out by squeezing the spinach. Place the spinach into a bowl. Add the onions and mushrooms to the bowl. Add the rest of the ingredients and combine. Pour the mixture into the greased casserole dish. Bake for 45 minutes to an hour. The top should look lightly brown and the cheese melted.