Vegetable Tian ( Barefoot in Paris Ina Garten)

Good olive oil
2 large yellow onions, cut in half and sliced
2 cloves garlic, minced
1 pound Yukon gold potatoes, unpeeled
3/4 pound zucchini
1 1/4 pounds medium tomatoes (I used plum tomatoes)
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1 tablespoon fresh thyme leaves, plus extra sprigs
2 ounces Gruyere cheese, grated
3 tablespoons Panko crumbs (my addition)

Preheat the oven to 375 degrees F.

Brush a 9x13x 2-inch baking dish with olive oil.  Ina medium saute pan, heat 2 tablespoons of olive oil and cook the onions over medium-low heat for 8 to 10 minutes, until translucent.  Add the garlic and cook for another minute.  Spread the onion mixture on the bottom of the baking dish.

Slice the potatoes, zucchini, and tomatoes in 1/4-inch-thick slices.  Layer them alternately in the dish on top of the onions, fitting them tightly, making only one layer.  Sprinkle with salt, pepper thyme leaves, and thyme sprigs and drizzle with 1 more tablespoon of olive oil.  Cover the dish with aluminum foil and bake for 35 to 40 minutes, until the potatoes are tender.  Uncover the dish, remove the thyme sprigs, sprinkle with cheese on top, and bake for another 30 minutes, or until browned.  Serve warm.

Can be made ahead of time, refrigerated and reheated at serving time.