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1
Preheat the oven to 350.
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2
Arrange the baguette slices on a large baking sheet and drizzle lightly with olive oil.
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3
Season the bread with salt and pepper and bake for about 6 minutes, until crisp and golden brown.
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4
In a 10-inch ovenproof skillet, heat 2 tablespoons of the olive oil.
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5
Add the zucchini, onion and thyme, season with salt and pepper and cook over moderately high heat, stirring a few times, until just tender, about 5 minutes.
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6
Add 1/4 cup of the broth and the heavy cream and simmer over moderate heat until slightly thickened, about 3 minutes.
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7
Season with salt and pepper and transfer half of the zucchini mixture to a plate and reserve.
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8
Spread the remaining zucchini in an even layer in the skillet.
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9
Sprinkle with 2 tablespoons of the Gruyere and 1 tablespoon of the Parmigiano-Reggiano and top with a layer of toasted baguette slices.
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10
Spread the reserved zucchini mixture over the toasts and sprinkle with an additional 2 tablespoons of Gruyere and 1 tablespoon of Parmigiano-Reggiano.
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11
Arrange alternatively slices of tomato and baguette on top in concentric circles.
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12
Sprinkle with the remaining 1/4 cup Gruyere and 3 tablespoons of grated cheese.
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13
Drizzle with the remaining 2 tablespoons of olive oil and season with salt and pepper.
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14
Carefully pour the remaining 1/4 cup of broth around the edge of the skillet and over the top.
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15
Bake for about 35 minutes, until the top is richly browned and the tomatoes have released their juices.
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16
Let stand for 10 minutes before serving.