Zucchini and squash au gratin is tender rounds of zucchini and yellow summer squash in a garlicky cream sauce, baked under a crisp, golden topping of panko and Parmesan. It is the side dish for late summer, when the garden gives you more squash than you can use, and it is good next to chicken, steak or fish.
How to make zucchini and squash au gratin: Cook sliced zucchini, yellow squash and shallots in butter in a large skillet until crisp-tender. Add garlic, then cream, and cook until thickened. Stir in half the panko and Parmesan, spoon into a baking dish, top with the rest and bake at 450°F for 8 to 10 minutes until golden.
Why You’ll Love It
- Not soggy. The squash is cooked in an open skillet first, so its water cooks off before it bakes.
- A crisp top. Panko and Parmesan brown fast in a hot oven.
- Quick. About 35 minutes from cutting board to table.
- Uses up the garden. Two zucchini and two yellow squash go into one dish.
Ingredient Notes
Zucchini and yellow summer squash. Two medium of each, cut into 1/4-inch slices. Even slices cook at the same rate.
Shallots and garlic. Two shallots and 4 cloves of garlic, both minced.
Butter. Two tablespoons, for the skillet.
Heavy whipping cream. A 1/2 cup. It is cooked down until thick.
Panko bread crumbs. One cup, divided: half goes into the vegetables and half on top.
Parmesan cheese. A 1/2 cup, grated and divided the same way.
Sea salt and pepper. A 1/2 teaspoon of sea salt and 1/4 teaspoon of coarsely ground pepper.
Ingredients
- 2 tablespoons butter
- 2 zucchini, medium, cut into 1/4-inch slices
- 2 yellow summer squash, medium, cut into 1/4-inch slices
- 2 shallots, minced
- 1/2 teaspoon sea salt
- 1/4 teaspoon pepper, coarsely ground
- 4 cloves garlic, minced
- 1/2 cup heavy whipping cream
- 1 cup panko bread crumbs, divided
- 1/2 cup Parmesan cheese, grated, divided
How to Make Zucchini and Squash Au Gratin
1. Heat the oven. Preheat the oven to 450°F.
2. Cook the vegetables. Melt the butter in a large skillet over medium heat. Add the zucchini, yellow squash and shallots. Season with the salt and pepper. Cook, stirring, for 4 to 6 minutes, until the vegetables start to brown and are crisp-tender. Use the largest skillet you have so the vegetables are not crowded.
3. Add the garlic and cream. Add the garlic and cook for another minute. Add the cream and cook for 3 to 5 minutes, until thickened.
4. Add the crumbs and cheese. Remove the skillet from the heat. Stir in 1/2 cup of the panko bread crumbs and 1/4 cup of the Parmesan.
5. Top and bake. Spoon the mixture into an 11-by-7-inch or 2-quart baking dish. Sprinkle with the remaining bread crumbs and Parmesan. Bake for 8 to 10 minutes, until golden brown. Check the center with a food thermometer. Casseroles must reach 165°F, so keep baking if needed.
6. Serve. Let the gratin cool slightly so it can set up before serving.
How to Keep the Gratin From Getting Soggy
Summer squash is full of water, and that water is what turns a gratin soupy. This recipe deals with it on the stove, before the dish ever goes into the oven.
| Step | What to do | How it helps |
|---|---|---|
| The skillet | Use the largest one you have | Less crowding lets more water evaporate |
| The vegetables | Cook 4 to 6 minutes, until starting to brown and crisp-tender | They give up moisture but keep their shape |
| The cream | Cook 3 to 5 minutes, until thickened | A thick sauce goes into the dish, not a thin one |
| The crumbs | Stir half the panko into the mixture | The rest goes on top for the crust |
Do not cook the squash until soft in the skillet. Crisp-tender is the goal, because it still has 8 to 10 minutes in a 450°F oven ahead of it.
Tips for Success
How thick should I slice the squash?
A 1/4 inch. Keep the slices the same thickness so they cook evenly.
How do I know the gratin is done?
The top is golden brown and a food thermometer in the center reads 165°F. A golden top by itself is not enough, so check the temperature.
What size baking dish do I need?
An 11-by-7-inch dish or a 2-quart baking dish.
Why does the garlic go in after the vegetables?
The recipe adds it once the squash is crisp-tender and cooks it for only another minute before the cream goes in.
Should I serve it straight from the oven?
Let it cool slightly first. That short wait lets the gratin set up so it holds together on the spoon.
How Long Does It Take?
About 35 minutes: 25 minutes of prep, which includes slicing and the skillet cooking, and about 10 minutes in the oven. Give it a few minutes to cool slightly before serving. The recipe does not put a number on that.
Variations
Smoked Gouda. Some zucchini and squash gratins are finished with smoked Gouda on top instead of panko and Parmesan.
Cracker topping. There is also a style with a cracker topping and a sour cream, mayonnaise and egg filling.
Both are separate recipes with their own amounts, and neither is the cream version on this page.
Storage & Reheating
USDA FSIS says to refrigerate leftovers within 2 hours in shallow, covered containers and to use them within 3 to 4 days. Reheat leftovers to 165°F. I would not freeze this one: FSIS notes that cream sauces may separate after freezing.
What to Serve With It
For more ways to cook summer squash, try roasted garlic-Parmesan zucchini, squash and tomatoes, skillet zucchini and mushrooms, baked zucchini fries or garlic herb roasted potatoes, carrots and zucchini. If you like anything au gratin, there is ham and potato au gratin and the copycat steakhouse potatoes au gratin.
Frequently Asked Questions
How do you cook zucchini and squash so the gratin does not get soggy?
Cook the slices in a large, uncrowded skillet until crisp-tender, then thicken the cream before the mixture goes into the baking dish.
Can zucchini gratin be made without cream?
There are gratins made without cream, but this recipe is not one of them, and I do not have amounts for making it that way.
Can I use only zucchini or only yellow squash?
The recipe is written for two of each. I have no separate directions for using only one kind.
How many does it serve?
Six, as a side dish.
Final Notes
I use my widest skillet for this and keep the squash in a single loose layer, because crowded squash steams instead of browning. If you make it, leave a comment to tell me how it turned out or ask a question.
Zucchini and Squash Au Gratin
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Ingredients
- 2 tablespoons butter
- 2 zucchini medium; cut into 1/4-inch slices
- 2 yellow summer squash medium; cut into 1/4-inch slices
- 2 shallots minced
- 1/2 teaspoon sea salt
- 1/4 teaspoon pepper coarsely ground
- 4 cloves garlic minced
- 1/2 cup heavy whipping cream
- 1 cup panko bread crumbs divided
- 1/2 cup Parmesan cheese grated; divided
Instructions
- Preheat the oven to 450°F.
- Melt the butter in a large skillet over medium heat. Add the zucchini, yellow squash and shallots. Season with the salt and pepper. Cook, stirring, for 4 to 6 minutes, until the vegetables start to brown and are crisp-tender. Use the largest skillet you have so the vegetables are not crowded.
- Add the garlic and cook for another minute. Add the cream and cook for 3 to 5 minutes, until thickened.
- Remove the skillet from the heat. Stir in 1/2 cup of the panko bread crumbs and 1/4 cup of the Parmesan.
- Spoon the mixture into an 11-by-7-inch or 2-quart baking dish. Sprinkle with the remaining bread crumbs and Parmesan. Bake for 8 to 10 minutes, until golden brown. Check the center with a food thermometer. Casseroles must reach 165°F, so keep baking if needed.
- Let the gratin cool slightly so it can set up before serving.
