for the dough • large egg yolks, room temperature • large whole egg, room temperature • sugar, approximately 1/4 cup • unsalted butter, melted • cold butter for lubricating baking dish • buttermilk, room temperature • all-purpose flour divided into 10 ounces, 4 ounces and 1 ounce batches • rapid rise yeast, approximately 1/4 ounce • kosher salt • for the filling • light brown sugar •