Tomato and Brie Tart

Name: Tomato and Brie Tart
Ingredients: Unbleached all-purpose flour, for dusting; 8 ounces puff pastry (or 1 sheet of a 17.3-ounce package), preferably all-butter; 12 ounces mixed tomatoes, such as beefsteak and heirloom, cut into ¼-inch-thick rounds; Kosher salt and freshly ground pepper; 2 tablespoons Dijon mustard; 4 ounces Brie, sliced ¼ inch thick; 1 tablespoon capers, drained; 1 teaspoon fresh thyme leaves, plus sprigs for serving (optional); 1 tablespoon extra-virgin olive oil; Dressed salad greens, for serving (optional)