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Add flour and 1 tsp salt to food processor, add butter and pulse until butter is the size of peas
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Add egg yolks and pulse to combine, then add ice water and pulse until dough forms
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Roll dough into flat disk on floured counter, wrap in plastic and refrigerate for 30 min
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Preheat oven to 400F, line pan with sheet paper
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Place sliced tomatoes into large bowl and toss with oil and a mixture of parsley, basil, garlic, thyme, 1 tsp salt, and 1 tsp pepper that is finely minced
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Roll dough out to 11x17 inch rectangle on floured surface, transfer to sheet pan
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Line dough with foil and place something heavy on top, bake for 15 min
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Remove foil, pierce dough with fork in many places, and bake another 8-10 minutes until lightly browned
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Allow crust to cool for 15 minutes, lower oven to 375F
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Brush mustard over dough, add layer of Gruyere (reserve 1/2 cup) and add 1/2 cup Parmesan
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Place overlapping rows of tomatoes across the cheese, top with remaining strained herb mixture
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Add remaining cheese to top, bake for 30 minutes