Preheat your oven to 375°F. Line a rimmed baking sheet with unbleached parchment paper and set it aside.
In a large bowl, place the flour, xanthan gum, nonfat dry milk, baking powder, baking soda and salt, and whisk to combine well.
Add the chopped and chilled butter, and toss to coat it in the dry ingredients.
Flatten each chunk of butter between your thumb and forefinger.
Create a well in the center of the dry ingredients and add the milk or cream, and mix until the dough begins to come together. If necessary, press together into a dough with floured hands, handling it as little as possible.
Turn out the dough onto a lightly floured piece of unbleached parchment paper and press into a disk.
Place another piece of unbleached parchment paper on top of the dough, and roll out into a rectangle that is about 1 inch thick.
Remove the top piece of parchment paper, sprinkle lightly with flour, and fold the dough over on itself like you would a business letter.
Sprinkle the dough again lightly with flour, replace the parchment paper and roll out the dough once again into a rectangle about 1 inch thick.
Once more, remove the top piece of parchment paper, sprinkle lightly with flour, and fold the dough over on itself like you would a business letter.
Sprinkle the dough again lightly with flour, replace the parchment paper and roll out the dough, but this time into a disk about 1-1/2 to 2 inches thick. Peel back the top piece of parchment paper, and, using a floured 3 1/2-inch cookie or biscuit cutter, cut out rounds of dough.
Place the rounds about 2 inches apart from one another on the prepared baking sheet. Gather and reroll the scraps, and cut out as many more round of dough as possible, as place on the prepared baking sheet.
Chill in the freezer until firm (about 10 minutes).
Bake the biscuits. Remove the baking sheet from the freezer place it in the center of the preheated oven.
Bake until the biscuits are puffed, very fragrant and lightly golden brown around the edges (about 20 minutes).
Remove from the oven and allow the biscuits to cool briefly on the baking sheet. While the biscuits are cooling, finish making the gravy.
Make the gravy.
Place the sausage in a heavy-bottom skillet and cook over medium heat, breaking up any large clumps and stirring occasionally, until the sausage is lightly golden brown and cooked through.
Drain the rendered pork fat away from the cooked pork and transfer it to a separate, small bowl. Remove the cooked pork from the skillet and set it aside.
Return about 4 tablespoons of the rendered pork fat to the skillet, add the xanthan gum-free flour blend, and mix to combine.
Cook slowly over medium-low heat, whisking frequently, until the mixture is light golden brown and nutty smelling (about 3 minutes, and it will go from very blond to golden brown and fragrant quite suddenly, so pay close attention).
Add the stock, and whisk to combine. The mixture will clump at first, but keep whisking.
Add the milk and cream, and increase the heat to medium.
Bring the mixture to a simmer and cook, whisking very frequently, until thickened (about 5 minutes).
Stir in the salt, pepper and the optional nutmeg to taste, add some of the cooked pork, and serve over the warm biscuits immediately.