Make the filling:
- Preheat the oven to 350°F.
- Place the tomatoes on a clean dish towel in a single layer and sprinkle with about 2 teaspoons of salt, making sure all the tomatoes are covered in an even layer. Let them stand for 10 minutes, allowing the excess liquid to drain out.
- While the tomatoes are draining, heat the oil in a medium skillet over medium heat.
- Add the onion and sauté for 3 to 4 minutes, until translucent and tender.
- Season with 1¼ teaspoons salt and 1¼ teaspoons pepper. Set aside.
- In a medium bowl, mix together the Gruyère, Parmesan, and mayonnaise.
Assemble the pie:
- Layer the ingredients in the partially baked pie crust, starting with about a quarter of the cheese mixture, then all the tomatoes, onions, and herbs, seasoning each layer with pepper.
- Sprinkle the remaining cheese mixture on top.
Bake the pie:
- Place the pie on a baking sheet and bake on the center rack for 30 minutes, or until the cheese is bubbly.
- While it is still warm, wrap it up carefully in your favorite tea towel, take it to a park, and enjoy it outside in the sun on a blanket while you listen to the birds sing in the trees. It's a summertime dream to be enjoyed in the Natural State.