1. Whisk together the flour blend, sugar (if using) xanthan gum (if using), and salt.
2. Take half of the butter (3 slices) and cut these pieces in half once more. Work these small pieces into the flour mixture until it's crumbly "like cornmeal", with some larger, pea-sized chunks of butter remaining.
3. Take the remaining butter and work it into the flour with your fingers by flattening the butter pieces down between your thumb and forefinger. You should be able to see pieces of butter "about the size of dried cranberries" in the flour.
4. Sprinkle lemon juice over the flour/fat mixture and mix until dough begins to come together. Add ice water 1 tablespoon at a time, if necessary, to bring the dough mass together.
5. Dump dough out onto work surface and shape into a ball. Flatten into a round and wrap tightly in plastic wrap, then refrigerate for at least an hour, or as long as two days.
6. When you are ready to bake the pies, preheat the oven to 400°F and butter ten regular-sized (2 3/4- 3 inch diameter) muffin cups.
7. Remove chilled dough from the refrigerator, then allow to sit at room temperature until it's pliable (10-20 minutes). Unwrap the dough, then divide it into 8-10 equal pieces (I went with the 8, but I think I could have made the shells thinner if I wanted to make 10).
8. Press each piece of dough firmly and evenly into a muffin cup (you could roll the pieces out first, but I chose not to and it worked out just fine), then lightly prick the bottom of each shell with a fork. Cut small squares of foil so you can press a piece into each one, covering each mini pie shells.
9. Bake for 10-12 minutes, until the dough is pale golden in color. Set the pie shells aside to cool while you make the filling, and decrease the oven temperature to 350 degrees F.