In a large bowl, whisk together flour blend, salt, xanthan gum and baking powder. Using two knives, a pastry cutter or your hands, work in butter until mixture resembles coarse cornmeal (see Tips, below).

In a small bowl, whisk together egg and 1 tbsp (15 mL) ice water. Add to flour mixture and stir lightly with a fork. Add remaining water, 1 tbsp (15 mL) at a time, stirring until mixture begins to form a soft ball of dough.

Using your hands, gently shape dough into a ball. Wrap tightly in plastic wrap and refrigerate for about 20 minutes to rest.

Dust a clean work surface and rolling pin with flour. Turn out chilled dough and, using your hands, flatten into a disk. Sprinkle with flour and roll into a 12-inch (30 cm) circle about 1/4 inch (0.5 cm) thick, dusting with additional flour if needed to keep dough from sticking.

Dust circle with flour and roll loosely around rolling pin, then unroll over pie plate. Gently press dough into plate and patch any tears. Trim edges, leaving a 1/2-inch (1 cm) overhang. Pinch to form edges.

Fill and bake according to the recipe instructions for the pie you are making.