Martha Stewart Potato, Zucchini, and Tomato Gratin

Martha Stewart Potato, Zucchini, and Tomato Gratin is easy to build: mandoline-thin Yukon golds, zucchini, and ripe tomatoes layered with garlic and olive oil. Cheddar and fresh thyme turn it golden for a summer side next to grilled chicken or lamb.

Serve it warm or at room temperature with a green salad for a lighter vegetarian weeknight dinner. Slicing evenly is what decides the whole dish, so use a mandoline or you risk raw potato in the center.

Martha Stewart Potato, Zucchini, and Tomato Gratin

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Course: Side DishCuisine: American, FrenchDifficulty: Easy

Servings

6

servings

Prep time

40

minutes

Cooking time

1

hour 

Calories

145

kcal

Golden on top and tender within, with paper-thin layers of potato and zucchini that melt into each other under a bubbling cap of cheddar.

Ingredients

• 5 teaspoons extra-virgin olive oil
  

• 2 garlic cloves, minced
  

• 1 medium zucchini (about 8 ounces)
  

• 1 pound Yukon gold potatoes, peeled
  

• 2 vine-ripened or other ripe tomatoes (about ¾ pound), sliced into ¼-inch rounds
  

• 1/4 teaspoon coarse salt
  

• 1 teaspoon finely chopped fresh thyme
  

• 2 ounces finely grated Cantal or cheddar cheese
  

Directions

• Prep the dish and slice vegetables: Preheat oven to 375°F with rack in upper third. Coat an 8-inch (1 1/2-quart) gratin dish with 1 teaspoon oil, and sprinkle with garlic. Using a mandoline or a very sharp knife, slice zucchini as thinly as possible into rounds; repeat process with potatoes.
• Assemble the gratin: Arrange potatoes, zucchini, and tomatoes in overlapping layers around prepared dish, seasoning each layer with salt and pepper as you go. Drizzle with remaining 4 teaspoons oil, and sprinkle with thyme and cheese.
• Bake: Cover with foil; bake until potatoes are tender, 35 to 45 minutes. Remove foil; continue baking until top is golden brown, about 25 minutes more. Remove from oven, and serve immediately.

Tools for this recipe

• Benriner Japanese mandoline, OXO 4-sided box grater, Partanna Sicilian extra virgin olive oil, 1 liter. As an Amazon Associate I earn from qualifying purchases.

FAQs

Can I make this gratin without a mandoline?

A sharp chef's knife works if you take your time, but aim for slices no thicker than 1/8 inch. Uneven slices mean some pieces stay raw while others overcook, so go slow and keep a steady hand.

What cheese works best for this potato zucchini gratin?

The recipe calls for Cantal, a firm French cheese with a flavor between cheddar and Gruyere. Sharp cheddar is the easiest swap, and Gruyere or Comte will give you a nuttier, more complex melt.

How do I store leftover gratin?

Cover and refrigerate for up to 4 days, but skip the freezer since the zucchini and tomatoes turn mushy once thawed. Reheat in a 325°F oven for about 20 minutes so the edges crisp up again.

Can I assemble this gratin ahead of time?

Layer everything in the dish, cover tightly with plastic wrap, and refrigerate for up to 8 hours before baking. Add about 10 extra minutes of covered baking time since it starts cold from the fridge.

Can I use a different squash instead of zucchini?

Yellow summer squash is the closest swap and holds its shape the same way in the oven. Pattypan squash works too, though you will need to cut it into half-moons instead of rounds.