Herbed Squash Casserole

Herbed squash casserole is a baked dish of tender summer squash, creamy sauce, and a crispy topping that turns soft vegetables into something substantial. The squash releases water as it cooks, so you drain it before assembling to keep the casserole from becoming soupy. Fresh herbs brighten the whole dish without overpowering it.

Ingredients for Herbed Squash Casserole

Yellow squash and zucchini form the base, cooked until soft and drained to remove excess moisture. Butter and onion build a simple roux, while garlic adds depth. All-purpose flour thickens the sauce, whole milk and chicken broth make it creamy, and sharp cheddar cheese brings flavor and richness. Fresh thyme, fresh sage, and fresh basil season it brightly. Salt and black pepper balance everything. Panko breadcrumbs mixed with melted butter and more cheddar crisp up on top.

Why This Herbed Squash Casserole Works

Cooking the squash first and draining it removes the water it sheds as it heats, which is the most common reason this casserole turns watery and breaks apart when served. The pieces stay intact and absorb the creamy sauce instead of sitting in liquid.

The roux of butter and flour thickens the milk and broth so the sauce coats the squash without being thin or runny. The cheese melts into the sauce and adds a savory note that makes the mild squash taste more interesting.

Fresh herbs stirred in at the end keep their bright flavor instead of fading during the long bake. The buttered breadcrumb topping crisps in the oven and gives a textural contrast to the soft squash beneath.

Mistakes To Avoid

Skipping the step of cooking and draining the squash first is the fastest way to end up with a watery, soupy casserole that falls apart when you scoop it. Raw squash releases a lot of water as it bakes, and there is no way to drain it once it has started cooking.

Cutting the squash too thin or too thick means uneven cooking. Thin pieces turn mushy while thick ones stay hard. Half-moons about 1/4 inch thick cook through at the same rate and keep their shape.

Overcooking the roux or letting the milk scorch on the bottom of the pan gives the sauce a burnt or grainy taste. Keep the heat at medium and stir constantly so the flour cooks through without browning and the milk heats evenly.

Assembling the casserole and baking it right away leaves no time for the flavors to meld. Making it the day ahead and refrigerating it overnight lets the herbs and cheese season the whole dish more fully, though it will take about 10 extra minutes to bake from cold.

As an Amazon Associate, we earn from qualifying purchases.

Ingredients

• 2 pounds yellow squash, sliced 1/4 inch thick
• 2 pounds zucchini, sliced 1/4 inch thick
• 4 tablespoons butter
• 1 medium onion, diced
• 3 cloves garlic, minced
• 3 tablespoons all-purpose flour (24 grams)
• 1 cup whole milk
• 1 cup chicken broth
• 1 1/2 cups sharp cheddar cheese, shredded, divided
• 2 tablespoons fresh thyme, chopped
• 2 tablespoons fresh sage, chopped
• 2 tablespoons fresh basil, chopped
• 1 teaspoon salt
• 1/2 teaspoon black pepper
• 1 cup panko breadcrumbs
• 3 tablespoons butter, melted

Step-by-step Instructions

1. Bring a large pot of salted water to a boil over high heat. Add the yellow squash and zucchini and cook for 6 to 8 minutes, until just tender but not soft. Drain in a colander and let sit for 5 minutes.
2. Press the squash gently with the back of a spoon to release excess water. Set aside.
3. Preheat the oven to 350°F (175°C).
4. Melt 4 tablespoons butter in a medium saucepan over medium heat. Add the diced onion and cook for 3 to 4 minutes, stirring often, until softened and translucent.
5. Add the minced garlic and cook for 1 minute more, stirring constantly, until fragrant.
6. Sprinkle the flour over the onion and garlic and stir for 1 minute to coat evenly. The mixture should look like wet sand.
7. Pour in the milk and broth slowly, stirring constantly to prevent lumps. Keep stirring over medium heat for 4 to 5 minutes, until the sauce thickens and coats the back of a spoon.
8. Remove from heat and stir in 1 cup of the cheddar cheese until melted. Fold in the thyme, sage, and basil. Season with salt and pepper.
9. Spread the drained squash in a 9×13 baking pan. Pour the sauce over the top and stir gently to coat all the pieces.
10. Toss the panko breadcrumbs with 3 tablespoons melted butter and the remaining 1/2 cup cheddar cheese. Scatter the mixture evenly over the casserole.
11. Bake for 25 to 30 minutes, until the top is golden brown and the sauce bubbles at the edges. An instant-read thermometer inserted into the center should read 165°F (74°C).
12. Let rest for 5 minutes before serving so the casserole sets and holds together when scooped.