Sides / Casseroles & table breads
Zucchini Casserole with Creamy Gruyère Sauce
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Salt the zucchini and let it drain while you stir up the cream sauce, so the layers hold together instead of turning soupy. Gruyère melts through, panko toasted in butter crowns the top, and the dish gets scraped to the corners.
The short version
Salt sliced zucchini and let it drain 20 minutes, then pat it dry. Layer it with an onion-cream-Gruyère sauce, cover and bake at 400°F for 30 minutes. Uncover, add toasted panko and bake 5 minutes more.
What makes ours better
why ours wins the argument at dinner
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Salt and drain the zucchini. Salt pulls out about half the water before it can end up in the dish. This is the step that makes the casserole creamy rather than soggy.
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Use a cream sauce with sour cream. A quick sauce of onion, cream and sour cream coats every slice, and the sour cream adds a tang that cuts the richness.
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Toast the panko in butter first. Panko browned in a pan stays crisp on top of a wet casserole. Raw crumbs go pale and soggy in 5 minutes.
What you need
the stars of the show
- Zucchini2 pounds
- Unsalted butter1 tablespoon
- Heavy cream1 cup
- Dried thyme½ teaspoon
- Sour cream½ cup
- Shredded Gruyère1¼ cups
- Shredded mozzarella½ cup
- Panko breadcrumbs½ cup
Zucchini
Sauce
Topping
read it twice. buy it once.
Steps
go slow. the good part can’t be rushed.
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Salt the zucchini
Heat the oven to 400°F and butter a 2-quart baking dish. Toss the zucchini slices with 2 teaspoons salt in a large bowl, then spread them on a towel-lined sheet pan. Leave them for 20 to 30 minutes, until beads of water show on the surface.
About 20 min. Cook mode has a timer for this step.
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Dry the slices
Pat the zucchini firmly dry with paper towels, pressing out the water, and brush off any extra salt.
Do not rinse. You'd add back the water you just removed.
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Cook the onion
Melt 1 tablespoon butter in a large skillet over medium-high heat. Add the onion and cook until soft and just starting to color, 5 to 7 minutes. Stir in the garlic for 30 seconds.
About 6 min. Cook mode has a timer for this step.
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Make the sauce
Pour in the cream and add the thyme, salt and pepper. Simmer 3 minutes, until slightly thickened. Take the pan off the heat and stir in the sour cream and 1 cup of the Gruyère until smooth.
About 3 min. Cook mode has a timer for this step.
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Layer the dish
Spread half the zucchini in the baking dish, overlapping a little, then spoon half the sauce over it. Repeat with the rest. Scatter the remaining ¼ cup Gruyère, the mozzarella and the Parmesan over the top. Cover tightly with foil.
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Bake covered
Bake 30 minutes, until the zucchini is tender when poked with a knife and the sauce is bubbling at the edges.
About 30 min. Cook mode has a timer for this step.
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Toast the panko
While it bakes, melt 2 tablespoons butter in a small skillet over medium heat, add the panko and stir until golden, 2 to 3 minutes. Watch it closely.
About 3 min. Cook mode has a timer for this step.
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Finish and rest
Remove the foil, scatter the panko over the top and bake 5 minutes more, until the cheese is melted and golden. Rest 5 to 10 minutes before serving so the sauce thickens.
About 5 min. Cook mode has a timer for this step.
Good to know
the stuff I’d tell you over the phone
- Yellow summer squash works the same way, or use half and half.
- Make ahead. Assemble through the cheese (not the panko), cover and refrigerate up to 1 day. Add 5 to 10 minutes to the covered bake.
- Swap Gruyère for Swiss or sharp white cheddar, and Greek yogurt for the sour cream.
- Lower carb? Skip the panko, or use a spoonful of almond flour in the butter.
- Storage. Refrigerate up to 4 days. Reheat at 350°F until hot. Freezes up to 2 months, thawed overnight in the fridge.
Questions, answered
asked and answered at the kitchen counter
Why is my zucchini casserole watery?
Zucchini is about 95 percent water. Salting the slices for 20 to 30 minutes and patting them dry removes much of it. Covering the casserole while it bakes steams the zucchini without browning the top, and a 5-minute rest lets the sauce thicken.
Do I have to salt the zucchini?
Yes, if you want a creamy casserole. Skipping the salt step is the usual reason zucchini bakes turn soupy.
Can I make zucchini casserole ahead of time?
Yes. Assemble it without the panko up to a day ahead and keep it covered in the fridge. Toast the panko just before baking.
Can I use shredded zucchini?
Slices layer better and hold their shape. If you shred it, salt it, then wring it out in a towel, and bake uncovered for the full time.
What goes well with zucchini casserole?
Roast chicken, pork chops, baked ham or grilled sausages. It also pairs with a simple green salad. For a lighter squash dish, see cheesy squash casserole with buttery cracker topping.
From the table
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Published October 29, 2026.