Lightly grease a baking sheet, or line it with parchment., Whisk the dry ingredients in a bowl. Add the butter and work it into the dry ingredients until the mixture is unevenly crumbly; use your fingers, a pastry blender, or an electric mixer., Stir together the eggs, milk, and vanilla extract. Add to the dry ingredients and stir very gently, just until combined., Divide the dough into three pieces, and round each piece into a 4"-diameter, 1"-thick disc. Place the discs on a baking sheet, and put them in the freezer for 30 minutes; no need to cover them., Preheat the oven to 375°F., Using a sharp or serrated knife, divide each chilled disc in half around its circumference. Spread the bottom half with the filling of your choice, then place the other half of the dough on top, pressing it down gently., Place the rounds on the prepared baking sheet. Brush with milk or water, and sprinkle with coarse sugar., Bake the dough rounds for about 28 minutes, until they're golden brown and a toothpick inserted into the center of one comes out clean., Remove the scones from the oven, and set the pan on a cooling rack. After 10 minutes, cut each disc into six triangular wedges., Serve scones warm, or at room temperature. Wrap any leftovers and store at room temperature for a day or so; freeze for longer storage.