Make the dough: in bowl of stand mixer with paddle attachment place flour, xanthan gum, buttermilk powder, yeast, cream of tartar, baking soda, and sugar; whisk with hand whisk to combine; add salt then whisk again; add the cider vinegar, butter, and egg then mix to combine well
With the mixer on low speed, slowly add water; once all the water is added turn the mixer up to high and let mix for 3 minutes; the dough will be moist but keep mixing until dough pulls away from the sides of the bowl
Put dough on floured surface; knead until smooth; divide the dough in half, place one half under a towel to prevent it from getting dried out Use a rolling pin covered lightly with flour, roll the remaining half of the dough into a rectangle shape ½ inch thick and 9 inches wide by 12 inches long
Using an offset spatula spread the softened butter all over the rectangle leaving a 1 inch border on every side; sprinkle the brown sugar evenly on top of the butter and pat the brown sugar down lightly with your fingers to help it stick to the butter; sprinkle the cinnamon evenly on top of the sugar
Starting at the short side, roll the dough tightly into a log; using a piece of thread, cut rolls into rolls 2 inches wide; place the rolls in prepared baking pan 1 inch apart; press the rolls down ⅓ of the way down; repeat this entire process with the other half of the dough
Cover pan with lightly oil plastic wrap and set in warm area allowing it to rise, about 1 hour
Preheat oven to 350F; remove plastic wrap; bake for 25minutes until golden brown; allow to cool to room temperature
In small bowl, combine powdered sugar and milk; mix until a thick paste forms; add more milk by a ¼ teaspoon until the glaze slowly falls off spoon; drizzle glaze over rolls