2 1/4 cups unbleached all-purpose flour
3 teaspoons salt, divided
1 cup cold unsalted butter, cut into cubes
3/4 cups sour cream
5 to 8 tablespoons ice water
2 1/2 pounds assorted red and yellow tomatoes, divided
1 3/4 cups grated Gruyère cheese
1/2 cup grated Parmesan cheese
3/4 cup mayonnaise
1 egg, beaten
1/2 cup loosely packed fresh basil leaves, cut into chiffonade (long, thin strips)
1 tablespoon fresh thyme, chopped
1/4 teaspoon pepper
1 cup sweet yellow onion, chopped
Process the flour and 1 teaspoon of the salt in a food processor, just until blended. Add the butter and pulse until the mixture resembles coarse meal. Remove to a bowl. Mix in the sour cream. Add the ice water 1 tablespoon at a time, mixing by hand until the dough forms a ball. Knead the dough 4 or 5 times. Wrap in plastic wrap and chill for 30 minutes.
Roll out the dough into a 13-inch circle on a floured surface. Fit into a 9-inch fluted tart pan with 2-inch sides and a removable bottom, trimming the edge. Chill for 30 minutes.
Cut the tomatoes into 1/4-inch slices and remove the seeds. Reserve 1/2 pound of the tomato slices. Arrange the remaining slices on paper towels. Sprinkle with 1 teaspoon of the salt. Let stand for 30 minutes. Pat dry with paper towels.
Preheat the oven to 425 degrees. Combine the Gruyère cheese, Parmesan cheese, mayonnaise, egg, basil, thyme, remaining 1 teaspoon salt and pepper in a bowl and mix well.
Spread the onion over the bottom of the pie shell. Dollop 1/3 of the cheese mixture over the onion. Arrange half of the salted tomatoes over the cheese mixture, overlapping the slices. Repeat the layers of cheese mixture and tomatoes. Dollop with the remaining cheese mixture. Top with the reserved tomatoes, overlapping the slices.
Place the pie on a baking sheet. Bake for 40 to 45 minutes or until the crust is brown and the filling is hot and bubbly, covering the outer rim of the crust with a foil ring or crust shield if the crust browns too quickly. Let stand at room temperature to cool completely. Garnish with basil chiffonade.
Recipes and photos courtesy of the Junior League of Denver