Preheat oven to 420°F. Set aside a 9-inch pie pan.
Sift dry ingredients into a mixing bowl. With a pastry blend, cut in shortening until the mixture looks like meal.
Mix milk and vinegar (or lemon juice) together. Stir with a fork until dough is soft and nicely moistened. Sprinkle rice flour on a counter and rolling pin. Put half the dough on the counter and roll out just a little larger than the 9-inch pan. Cut into 6 pieces and use a large spatula to carefully slip one piece at a time onto the pie plate. Repeat until all pieces have been used and edges line up. Seal edges with fingertips.