- Combine flour, xanthan gum (if using), and salt into medium bowl. Whisk to combine very well. 
- In bowl of a stand mixer, add 1 cup of flour mixture and yeast. Mix well. 
- Combine 1 cup water and oil; heat to 120-130ºF; add to flour mixture in mixer bowl. Blend at low speed until moistened; beat 2 minutes at medium speed. 
- Add remaining flour mixture. Start mixing on low speed, slowly add remaining water, 1 tablespoon at a time, until dough comes together. Mix at medium speed for 2 minutes, or until a soft dough forms and dough leaves the sides of the bowl. 
- Preheat oven to 400ºF. Lightly flour fingers and work surface with gluten free flour. Turn dough out onto work surface and flatten and shape as desired. (If making 2 pizzas, divide dough in half first, then proceed with shaping crusts.) You can use a floured rolling pin to get the round shape started, if you like. This dough works best patted or rolled out as a fairly thin crust pizza. Transfer dough to greased pizza pan(s) or baking sheet(s). 
- Spread prepared sauce on pizza(s). Add toppings and shredded cheese as desired. Do not allow dough to rise. Optional: Brush outer edges of dough with melted butter and sprinkle lightly with dried parsley or Italian herbs. 
- Bake at 400°F until edges are crisp and light golden brown, and cheese is melted: about 20 minutes for 8-inch pizzas, about 35 minutes for a large 15 to 16-inch pizza. Remove from oven and serve immediately. Store leftovers covered tightly in the refrigerator. Pizza reheats best in the oven or in a skillet.