Place the yeast in 1/2 cup warm water-1/2 cup milk along with 1 tablespoon sugar. Let stand for about ten minutes. (I use hot water and cold milk - hot+cold=warm)
In a stand mixer (or use your muscles) mix together the brown rice flour, tapioca starch, baking powder, xanthan gum, the rest of the sugar, and the salt together until well combined.
Mix together the yeast mixture, the softened butter (not melted!), the eggs, and the apple cider vinegar.
Add the additional warm water while mixing to get the right consistency. We're looking for something like stiff cake batter. It will be spoon-able, not knead-able like wheat breads.
Spread into two greased bread pans, about half full. One option I use regularly is to make a loaf of bread, a pizza crust, and use any leftover for breadsticks.
Let sit in a warm area for 20-40 minutes, depending on room temperature. Keep and eye on it as you don't want the bread in the pan to get too high as it will bake over the sides and fall to the bottom of the oven. I like to turn my stove on just enough to warm it, turn it off, and then place the pans inside for the bread to rise.
Bake at 350 degrees for about 25 minutes, or until 190 degrees in the center.