Preheat your oven to 375°F. Grease an 8-inch square baking dish lightly and set it aside. This is one of the very few instances where a glass baking dish works quite well, but you can use any square baking dish you like.

First, make the biscuit dough. In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, baking soda, salt and sugar, and whisk to combine well. Add the grated butter, and toss to combine, breaking up any clumps of butter. Create a well in the center of the dry ingredients, add the buttermilk and mix until just combined. The mixture should be relatively soft for biscuit dough. Turn the dough out onto a large piece of plastic wrap, press together and wrap tightly. Refrigerate the biscuit dough for at least 10 minutes and up to 5 days. Once the dough has chilled, turn it out onto a lightly floured surface, sprinkle lightly with more flour and roll out into an approximately 8-inch rectangle. Cut out a 1/2-inch square or other shape in the very center of the dough (to allow steam to escape during baking), place it on a flat surface and then in the freezer to chill while you prepare the filling.

Prepare the peach filling. In a large bowl, place the peaches, sugar, cornstarch, salt, cinnamon, optional nutmeg and almond (or vanilla) extract, and toss to combine completely. Transfer the peaches to the prepared baking dish and spread into an even layer. Place the baking dish on a piece of foil, then on a rimmed baking sheet and place the baking sheet in the oven. Bake for 10 minutes to begin to soften the peaches.

Top the peaches and bake. Remove the baking dish from the oven and place on a heatproof surface. Remove the pastry topping from the freezer and place it on top of the peaches in the baking dish. Return the dish to the oven and bake for 15 minutes. Remove the dish from the oven, brush the top evenly with the melted maple syrup and butter mixture, and return to the oven to finish baking (about 20 minutes). The dish is done when the filling is bubbling and the top is golden brown all over. Remove from the oven and allow to cool for 15 minutes before serving with vanilla ice cream (of course).