Blueberry Galette

Name: Blueberry Galette
Ingredients: 1/2 recipe Cornmeal Tart Dough (see below); 3 cups blueberries; 1/3 cup granulated sugar; 1 tablespoon all-purpose flour, plus more for rolling out dough; 1 tablespoon fresh lemon juice; 2 tablespoons Demerara sugar; 10 tablespoons (1 1/4 sticks) unsalted butter, at room temperature; 3/4 cup sugar; 1/4 cup buttermilk; 3/4 teaspoon pure vanilla extract; 1/2 cup yellow cornmeal or fine polenta; 1 1/2 cups unbleached all-purpose flour; 1 teaspoon kosher salt