Add flour, sugar, yeast, xanthan gum, and salt to the bowl of an electric mixer or a large glass bowl if using a hand held mixer. Mix on low to combine. With the mixer on low speed, drizzle in water then add the butter, egg, and vinegar. Once the batter is smooth turn the speed up to medium then beat for 3 minutes, scraping the sides down once. Batter will be the consistency of thick cake batter.

Spray a 9" glass pie pan with nonstick spray then use a 2" ice cream scoop to scoop the dough into the pan. Wet your fingertips with water then gently smooth the tops of the rolls. Cover pan with a tea towel then set in a warm place to rise for 45 minutes to 1 hour (I use my oven's "bread proof" setting, or place the pan on a heating pad set to low.)

Preheat oven to 400 degrees then bake rolls for 23-25 minutes or until the internal temperature of the rolls reaches 200 degrees. Check rolls around the 16 minute mark - if the tops are browning too fast, gently place a piece of foil on top of the pan then continue baking. Serve immediately - best if consumed within a few hours.