1 savory pie crust
3 tablespoons olive oil
2 large yellow onions
1 teaspoon salt
2 teaspoons minced garlic
2 large ripe tomatoes, like Beefsteak or Big Boy (about 1 pound)
1 cup grated Gruyere cheese (2-1/2 ounces)
3 tablespoons pesto
  freshly ground pepper
1/4 cup grated Parmigiano Reggiano cheese ((1/2 ounce))
1 large egg yolk
1 tablespoon milk
2 tablespoons extra-virgin olive oil (as optional garnish)
  fresh basil leaves (cut into thin ribbons or chiffonade, as optional garnish)