Maple Buttermilk Tart

Name: Maple Buttermilk Tart
Ingredients: 1 cup all-purpose flour, plus more for dusting; 2 tablespoons fine stone ground cornmeal; 2 tablespoons confectioners' sugar; 2 tablespoons superfine sugar; Pinch fine salt; 6 tablespoons cold unsalted butter, cut into 6 pieces; 1 large egg yolk, lightly beaten; Granulated or sanding sugar, for garnish, optional; 2/3 cup maple sugar; 2 tablespoons all-purpose flour; 5 tablespoons butter, melted and slightly cooled; 3/4 cup buttermilk; 1 teaspoon vanilla extract; 2 large eggs, lightly beaten