French Onion Soup Pizza

Name: “French Onion Soup” Pizza
Ingredients: 3 tablespoons olive oil, divided, plus more for baking sheet; 6 large shallots, thinly sliced (about 4 cups); ½ teaspoon kosher salt; 2 teaspoons balsamic vinegar; 1 pound store-bought pizza dough, at room temperature; 4 ounces Gruyère cheese, shredded (about 1 cup); ½ cup whole-milk ricotta cheese; 1 tablespoon chopped fresh flat-leaf parsley; 1 teaspoon fresh thyme leaves