INGREDIENTS
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1 1/4 cups all-purpose flour
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1/4 cup cold vegetable shortening, cut into pieces
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4 tablespoons cold unsalted butter, cut into pieces
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1/2 teaspoon fine sea salt
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3 to 4 Tbsp. ice-cold water
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2 1/4 pounds assorted heirloom tomatoes, thinly sliced
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1 1/4 teaspoons kosher salt, divided
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1 sweet onion, chopped
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1 1/4 teaspoons freshly ground pepper, divided
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1 tablespoon canola oil
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1/2 cup assorted chopped fresh herbs (such as chives, parsley, and basil)
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1/2 cup freshly grated Gruyère cheese
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1/2 cup freshly grated Parmigiano-Reggiano cheese
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1/4 cup mayonnaise