This Maple Buttermilk Pie has a creamy, smooth filling that is the perfect combination of tangy and sweet. Bake it up in a hearty Spelt Pie Crust with decorative maple leaves for a festive look. It’s crucial to bake the pastry fully before pouring in the filling, and to brush it with a whisked egg white while it is still hot.  Custards are baked at a low temperature so it would be impossible for the crust to actually bake with the filling inside, so be sure to follow the instructions for blind baking the crust. The brushed on egg white helps create a barrier between the filling and the crust. This helps keep the pie crust crisp after the custard has been baked.