1 tsp xanthan gum (if using GF Mama's, omit if your flour contains xanthan gum)
1 T baking powder
1/2 tsp baking soda
1/4 tsp salt
1/2 tsp cream of tartar
1/3 cup club soda or unflavored, unsweetened, sparkling water
Melt 1/3 cup butter in a medium bowl in the microwave. Begin with 10 seconds, remove and stir. Butter should be barely melted.
Whisk sour cream and sugar into melted butter until smooth.
Add flour, baking powder, baking soda, salt and cream of tartar and stir with a fork until mixture resembles coarse crumbs.
Add sparkling water and stir until mixture comes together. It should be fairly sticky.
Lightly flour counter top with about 2 tablespoons more flour mix and turn dough onto counter, turning to fully coat. Be careful not to mix the flour into the dough.
Flatten with your hands into a circle about 3/4" thick.
Fold in half to form a half circle, then in half again to form a triangular shape, and pat to 3/4" thickness again.
Repeat the last step. This folding is what creates the flaky, layered effect.
Cut into circles with biscuit cutter or large cup and arrange in a round cake pan so the biscuits are so close they are almost touching.
Preheat oven to 425°.
When oven is preheated, bake biscuits for 7-10 minutes. Remove biscuits just as edges begin to turn a golden brown and be sure not to overcook or they won't turn out so flaky and soft. Pry biscuit in half horizontally with a fork to see if it's done.
These are best served warm. Store any leftovers (if you happen to have any!) in a sealed bag at room temp for up to 2 days. You can also freeze. To reheat, wrap in foil and place in 300° oven about 5-10 minutes, or microwave individual biscuits about 25 seconds on 50% power. I've also made a double batch and wrapped half the cooled biscuits in foil to store in the freezer.