Crunchy Cornmeal and Tomato Galette

Ingredients

• 1 cup all-purpose flour, frozen for 1 hour
• 1/4 cup yellow cornmeal or polenta, frozen for 1 hour
• Coarse salt
• 8 tablespoons unsalted butter, cut into 1/2" pieces, frozen for 1 hour
• 3 tablespoons sour cream
• 1 teaspoon lemon juice
• 3 ounces coarsely grated mozzarella
• 3 ounces coarsely grated fontina
• 1/4 cup basil leaves, cut into thin strips
• 3 ripe but firm medium tomatoes, cored, thinly sliced
• Freshly ground black pepper