Potato, Onion, Gruyere Galette – Fustini's Oils & Vinegars

Ingredients

• 1 Flaky Tart Dough
• 1½ tablespoons Fustini’s Tuscan herb olive oil, plus 1 tablespoon for drizzling
• 1 large onion (12 ounces), thinly sliced
• ½ teaspoon finely chopped fresh thyme or rosemary
• ¼ teaspoon plus 1 pinch Fustini’s Flaky Sea Salt
• Black pepper
• 4 ounces Gruyere cheese, coarsely grated
• 1-pound red potatoes washed (left unpeeled) and cut into ¼-inch-thick slices
• 1 egg, lightly beaten
• Crème fraiche, for serving (optional)