Preheat oven to 500 degrees.

Combine the white rice flour, tapioca starch, sweet rice (glutinous) flour, powdered milk, sugar, salt, baking powder, and baking soda in a food processor. Pulse several times to combine. Add the butter and shortening and pulse several times until the mixture resembles coarse crumbs with some larger pieces. Add the egg and buttermilk, pulse to combine. Flour a work surface generously with sweet rice flour, dump the dough onto the flour and knead several times until the dough is no longer sticky.

Pat the dough into a circle a full 1 inch thick; the circle will not be very large in diameter. Cut out 3 inch biscuits using a well-floured cookie cutter or the top of a drinking glass. Place the biscuits into a cast iron skillet or non-stick 9 inch round cake pan. Reform the scraps and cut until the dough is used, you should have seven 3 inches by 1 inch biscuits.

Bake at 500 for 5 minutes then reduce the temperature to 450 and bake another 15 – 20 minutes or until a light golden brown on top. Brush with melted butter if desired and serve with jam.