This summer squash casserole is a southern classic made with seasonal fresh zucchini and yellow squash! The cheesy filing is topped with crispy french fried onions for the perfect side dish! Serve at a summer cookout, family dinner, or whenever your garden is overflowing with squash!
I know this is called "summer squash casserole" but it's also one of my favorite sides to serve at Thanksgiving dinner!
You might also like this fresh green bean casserole or this zucchini risotto!
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Ingredient Notes
You just need a few ingredients to make this zucchini and yellow squash casserole!
Squash - Both zucchini and yellow squash (also called crookneck squash) are considered "summer squash", so I usually use both! However, you can also use just one or the other, or substitute gold zucchini or romanesco squash! Any combination will work, you just need about 2 pounds total.
Greek Yogurt - For the filling I like to use plain full-fat Greek yogurt for a little extra protein in the casserole, but you can also substitute sour cream!
Cheddar Cheese - I prefer sharp white cheddar, but use whatever you like best! Colby jack or gruyere would also be delicious! I also recommend using blocks of cheese and shredding it yourself as opposed to pre-shredded cheese because it melts more smoothly in the squash casserole.
Eggs - The eggs help add structure to the casserole filling.
Cayenne Pepper - I love adding just a little bit of cayenne for some added flavor and heat! But just leave it out if you prefer.
French's Fried Onions - Confession: I love eating french fried onions straight out of the can! They're my favorite topping for literally any type of casserole! But I also love making my own crispy fried onions for when I want this summer squash casserole to be 100% from scratch. In the recipe notes I've also included instructions for a buttery Ritz cracker topping if you prefer that!
The complete list of ingredients and amounts is located in the recipe card below.
How to Make Squash Casserole
Thinly slice the zucchini and squash to about ¼ inch thick (I like using a mandoline to slice the squash quickly).
You need about 2 pounds of total squash, which is equivalent to about 2 medium zucchini and 2 medium yellow squash. After the squash is all sliced, you should have about 6 cups total.
Preheat the oven to 375°F.
In a large skillet over medium high heat, saute the onion and garlic in 1 tablespoon of butter for about 5 minutes or until softened. Then transfer to a large mixing bowl.
In the same skillet, melt the remaining 2 tablespoons of butter and then add in the sliced squash and ½ teaspoon of salt. Cook over medium heat, stirring frequently, for about 10 minutes or until the squash has softened.
Transfer to a colander and let all the excess liquid drain away for at least 5 minutes.
In the large mixing bowl with the cooked onions, add in the Greek yogurt, milk, eggs, 1 cup of shredded cheese, thyme, lemon juice, remaining salt, pepper, and cayenne and gently mix until fully combined.
Then add in the cooked and drained squash and stir gently to combine, making sure every piece of squash is coated in the sauce.
Transfer to a baking dish and sprinkle with the remaining shredded cheese, then bake uncovered at 375°F for 35 minutes.
If desired, top with french fried onions and bake for another 10 minutes or until golden brown and bubbling.
Remove from the oven and serve warm!
Enjoy this cheesy summer squash casserole along with your favorite roast chicken, steak, or as a side for Thanksgiving dinner!
Recipe Notes
While I have always been partial to topping this zucchini and yellow squash casserole with french fried onions, I know some people prefer a buttery cracker topping instead!
Optional Cracker Topping
- 1 sleeve Ritz crackers
- 2 tablespoons unsalted butter, melted
- Gently crush the Ritz crackers until you have small chunks.
- In a small bowl, combine the crushed crackers and melted butter.
- Make the casserole as directed and bake for 20 minutes. Then sprinkle the cracker mixture on top and bake for another 20-30 minutes or until golden brown and bubbling.
Recipe FAQ's
This casserole will last in the fridge for up to 4 days! Just note that the french fried onions will get soggy over time. So I like to top with extra french fried onions before serving!
Prep everything and place it in the casserole dish, then cover and refrigerate for up to 2 days. When you're ready to bake, remove from the fridge and let sit at room temperature for at least 30 minutes before baking (this ensures the casserole is fully cooked in the middle and also protects your casserole dish from cracking due to temperature change). Then bake and top with french fried onions as normal!
Cover with foil and reheat in the oven at 350°F for about 20 minutes. Add on extra french fried onions if desired! You can also reheat individual portions in the microwave if desired.
Cooking and draining the excess liquid from the zucchini and squash before assembling the casserole helps ensure the casserole will not get watery!
Tips for Success!
For best results I always recommend using weight measurements (especially when baking) because it's the most accurate. Kitchen scales are super affordable and also reduce the number of dishes you have to do! However, all my recipes also include US customary measurements for convince. Use this chart to convert measurements for common ingredients!
Substitutions: In all my recipes, I've included substitutions that I know will work, but I cannot guarantee results if you substitute ingredients that I have not recommended. [For example, granulated sugar and honey are indeed both sweeteners but they have very different properties so they can not always be swapped 1:1. Using honey in a cookie recipe that calls for granulated sugar will yield a giant mess.] In the recipe card you'll find links to the specific ingredients/brands that I use.
A note on salt: I almost exclusively use Diamond Crystal Kosher Salt because it's the best all-purpose salt for cooking and baking. If you're not using kosher salt, consult this handy guide for a conversion chart! When in doubt, if you're using table salt just reduce the amount by half for baked goods. When cooking, I prefer to under-salt because you can always add more! If you've over-salted, adding a little bit of acid (like lemon juice) can help.
More Side Dishes You Might Like!
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Recipe Card
Summer Squash Casserole
Special Equipment
- mandoline optional
Ingredients
- 2 medium zucchini, thinly sliced
- 2 medium yellow squash, thinly sliced
- 3 tablespoons unsalted butter, divided
- 1 small yellow onion, diced
- 2 cloves garlic, finely chopped
- 1 ½ teaspoons kosher salt, divided
- ½ cup plain full-fat Greek yogurt, substitute sour cream
- ½ cup whole milk
- 2 large eggs, beaten
- 1 ½ cups shredded cheddar cheese, divided
- 2 teaspoons fresh thyme , optional
- 1 teaspoon lemon juice
- ½ teaspoon black pepper
- ¼ teaspoon cayenne pepper, optional
- 1 cup french fried onions
Instructions
- Thinly slice the zucchini and squash to about ¼ inch thick (I like using a mandoline to slice the squash quickly). You need about 2 pounds of total squash, which is equivalent to about 2 medium zucchini and 2 medium yellow squash. After the squash is all sliced, you should have about 6 cups total.
- Preheat the oven to 375°F.
- In a large skillet over medium high heat, saute the onion and garlic in 1 tablespoon of butter for about 5 minutes or until softened. Then transfer to a large mixing bowl.
- In the same skillet, melt the remaining 2 tablespoons of butter and then add in the sliced squash and ½ teaspoon of salt. Cook over medium heat, stirring frequently, for about 10 minutes or until the squash has softened.
- Transfer to a colander and let all the excess liquid drain away for at least 5 minutes.
- In the large mixing bowl with the cooked onions, add in the Greek yogurt, milk, eggs, 1 cup of shredded cheese, thyme, lemon juice, remaining salt, pepper, and cayenne and gently mix until fully combined.
- Then add in the cooked and drained squash and stir gently to combine, making sure every piece of squash is coated in the sauce.
- Transfer to a baking dish and sprinkle with the remaining shredded cheese, then bake uncovered at 375°F for 35 minutes.
- If desired, top with french fried onions and bake for another 10 minutes.
- Remove from the oven and serve warm!
Notes
- 1 sleeve Ritz crackers
- 2 tablespoons unsalted butter, melted
- Gently crush the Ritz crackers until you have small chunks.
- In a small bowl, combine the crushed crackers and melted butter.
- Make the casserole as directed and bake for 20 minutes. Then sprinkle the cracker mixture on top and bake for another 20-30 minutes or until golden brown and bubbling.
Nutrition
The nutritional information on this website is only an estimate and is provided for convenience and as a courtesy only. The accuracy of the nutritional information for any recipe on this site is not guaranteed.
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