Au Gratin Yellow Squash and Zucchini is a creamy, cheesy, oven-baked vegetable casserole made with tender yellow squash, fresh zucchini, garlic, onions, and a rich cheese sauce. Topped with golden, bubbly cheese and a crispy breadcrumb crust, this comforting side dish is perfect for family dinners, holiday meals, or a delicious way to enjoy fresh vegetables.
Recipe Information
– Prep Time: 15 minutes
– Cook Time: 30–35 minutes
– Total Time: 50 minutes
– Servings: 6
– Course: Side Dish / Casserole
– Cuisine: American
– Cooking Method: Oven-Baked
Ingredients
For the Vegetables
– 2 medium yellow squash, thinly sliced
– 2 medium zucchini, thinly sliced
– ½ medium yellow onion, finely diced
– 2 cloves garlic, minced
– 1 tablespoon olive oil
– ½ teaspoon salt, or to taste
– ¼ teaspoon black pepper
For the Creamy Cheese Sauce
– 2 tablespoons unsalted butter
– 2 tablespoons all-purpose flour
– 1 cup whole milk
– ½ cup heavy cream
– 1 cup shredded sharp cheddar cheese
– ½ cup shredded Gruyère cheese
– ¼ teaspoon paprika
– ½ teaspoon Italian seasoning
– ¼ teaspoon garlic powder
– Pinch of nutmeg (optional)
For the Topping
– ½ cup shredded cheddar cheese
– ¼ cup grated Parmesan cheese
– ½ cup Panko breadcrumbs
– 1 tablespoon melted butter
– 1 tablespoon fresh parsley, chopped
Instructions
Step 1: Prepare the Oven
Preheat your oven to 375°F (190°C).
Lightly grease a 9 × 13-inch baking dish with butter or cooking spray.
Step 2: Prepare the Squash and Zucchini
Wash the yellow squash and zucchini thoroughly.
Slice them into thin, even rounds, approximately ¼ inch thick.
Place the sliced vegetables on paper towels and gently pat them dry to remove excess moisture.
Step 3: Sauté the Vegetables
Heat olive oil in a large skillet over medium heat.
Add the diced onion and cook for 2–3 minutes until softened.
Add minced garlic and cook for another 30 seconds.
Add the sliced yellow squash and zucchini. Season with salt and black pepper.
Cook for approximately 4–5 minutes, stirring gently, until the vegetables begin to soften.
Remove from heat and drain any excess liquid.
Step 4: Prepare the Creamy Cheese Sauce
In a medium saucepan, melt 2 tablespoons of butter over medium heat.
Whisk in the flour and cook for approximately 1 minute to remove the raw flour taste.
Gradually pour in the milk while whisking continuously to prevent lumps.
Add the heavy cream and continue stirring until the sauce begins to thicken.
Step 5: Add the Cheese and Seasonings
Reduce the heat to low.
Add 1 cup cheddar cheese and ½ cup Gruyère cheese.
Stir until the cheese melts into a smooth, creamy sauce.
Add paprika, Italian seasoning, garlic powder, and optional nutmeg.
Taste and adjust the seasoning as needed.
Step 6: Assemble the Casserole
Arrange the sautéed yellow squash and zucchini evenly in the prepared baking dish.
Pour the creamy cheese sauce over the vegetables.
Gently toss or spread the sauce so all the vegetables are coated.
Step 7: Prepare the Topping
In a small bowl, combine Panko breadcrumbs, melted butter, grated Parmesan cheese, and fresh parsley.
Mix until the breadcrumbs are lightly coated.
Sprinkle the remaining cheddar cheese over the casserole, followed by the breadcrumb mixture.
Step 8: Bake Until Golden
Place the baking dish in the preheated oven.
Bake uncovered for 25–30 minutes, until the sauce is bubbling and the vegetables are tender.
If the topping needs more color, broil for another 1–2 minutes, watching carefully to prevent burning.
Step 9: Rest and Serve
Remove the casserole from the oven.
Allow it to rest for approximately 5–10 minutes before serving. This helps the creamy sauce settle and makes serving easier.
Garnish with fresh parsley and serve warm.
Tips for the Best Squash and Zucchini Au Gratin
– Slice the vegetables evenly so they cook at the same rate.
– Pat the squash and zucchini dry before cooking.
– Do not overcook the vegetables during sautéing.
– Drain excess liquid to prevent a watery casserole.
– Freshly shredded cheese melts more smoothly than many pre-shredded varieties.
– Use Gruyère for a rich, slightly nutty flavor.
– Do not boil the cheese sauce after adding the cheese.
– Let the casserole rest before serving for a thicker consistency.
– For extra crunch, use Panko breadcrumbs.
Nutrition Information
Estimated per serving, based on 6 servings.
– Calories: 315 kcal
– Protein: 13 g
– Total Carbohydrates: 19 g
– Dietary Fiber: 3 g
– Total Sugars: 6 g
– Total Fat: 21 g
– Saturated Fat: 12 g
– Cholesterol: 60 mg
– Sodium: 520 mg
Nutrition values are approximate and may vary depending on cheese brands, portion sizes, and ingredient substitutions.
Nut Information & Allergen Details
Nut Information:
– Tree Nuts: No tree nuts intentionally included.
– Peanuts: None.
– Almonds: None.
– Walnuts: None.
– Cashews: None.
– Pecans: None.
– Pistachios: None.
– Hazelnuts: None.
– Coconut: None.
Other Allergens:
– Dairy: Contains milk, heavy cream, butter, cheddar, Gruyère, and Parmesan.
– Gluten: Contains wheat flour and Panko breadcrumbs.
– Eggs: Some packaged breadcrumbs may contain eggs.
– Soy: Check packaged cheese and breadcrumbs for soy-based additives.
– Sesame: Check packaged breadcrumbs for sesame ingredients.
Important Allergy Note: Gruyère naturally has a slightly nutty taste, but it does not necessarily contain tree nuts. Always check ingredient labels for possible cross-contamination.
Possible Substitutions:
– Gluten-Free: Use gluten-free flour and certified gluten-free breadcrumbs.
– Dairy-Free: Use unsweetened dairy-free milk, plant-based cream, butter, and melting cheese alternatives.
– Lower-Sodium: Choose reduced-sodium cheese, unsalted butter, low-sodium breadcrumbs, and reduce added salt.
– Lower-Carb: Omit the breadcrumbs and use a smaller amount of suitable cheese topping.
Frequently Asked Questions (Q&A)
Q1: Do I need to peel the yellow squash and zucchini?
No. The skins are tender and edible. Simply wash the vegetables thoroughly and slice them.
Q2: How do I prevent the casserole from becoming watery?
Pat the vegetables dry, sauté them briefly before baking, and drain any excess liquid. This is especially important because zucchini and yellow squash naturally contain a lot of moisture.
Q3: Can I use only yellow squash or only zucchini?
Absolutely! You can use either vegetable alone or combine them according to your preference.
Q4: What cheese works best for au gratin squash?
Sharp cheddar and Gruyère are excellent choices. Mozzarella, Monterey Jack, and Parmesan can also be used.
Q5: Can I make this casserole ahead of time?
Yes! Prepare the vegetable mixture and cheese sauce separately. Refrigerate them in covered containers and assemble shortly before baking. You can also assemble the casserole a few hours ahead and keep it refrigerated.
Q6: Can I make this recipe without breadcrumbs?
Yes! Simply leave out the breadcrumbs and add extra Parmesan or cheddar cheese on top for a delicious golden crust.
Q7: Can I use frozen zucchini and squash?
Fresh vegetables are recommended for the best texture. If using frozen vegetables, thaw them completely and squeeze out excess moisture before cooking.
Q8: Can I add other vegetables?
Yes! Mushrooms, spinach, onions, roasted red peppers, and thinly sliced potatoes can all be delicious additions.
Q9: How do I know when the casserole is ready?
The cheese sauce should be bubbling around the edges, the topping should be golden brown, and the vegetables should be tender when pierced with a fork.
Q10: Can I make this recipe in advance for a holiday dinner?
Yes! You can prepare the casserole a day ahead and refrigerate it. Add the breadcrumb topping just before baking for the best texture.
Q11: How should I store leftovers?
Allow the casserole to cool and transfer it to an airtight container. Refrigerate for up to 3–4 days.
Q12: Can I freeze squash and zucchini au gratin?
Freezing is possible, but it is not recommended for the best texture. Zucchini and yellow squash release water after thawing, and the creamy sauce may separate.
Q13: How do I reheat leftovers?
Reheat in an oven at 350°F (175°C) for approximately 15–20 minutes until heated through. Cover loosely with foil if the topping is browning too quickly.
Q14: Is this recipe vegetarian?
Yes, provided you use vegetarian-friendly cheeses made without animal-derived rennet.
Q15: Can I make this casserole keto-friendly?
Yes! Replace the flour with a suitable low-carb thickener, omit the breadcrumbs, and use full-fat cheese and cream. Check the nutritional values of your chosen ingredients.
Q16: Can I make the cheese sauce without flour?
Yes! You can make a cream-based cheese sauce using heavy cream and cream cheese, simmering gently until thickened.
Q17: Is this recipe suitable for a low-sodium diet?
It can be adapted by reducing added salt, choosing lower-sodium cheese, using unsalted butter, and selecting low-sodium breadcrumbs.
Serving Suggestions
This cheesy squash and zucchini casserole pairs beautifully with:
1. Garlic butter chicken breast.
2. Grilled lemon herb salmon.
3. Roasted turkey or chicken.
4. Garlic butter shrimp.
5. Grilled steak.
6. Mediterranean baked fish.
7. Fresh tomato and cucumber salad.
8. Roasted potatoes and steamed green beans.