Set aside a miniature muffin tin with 24 cups, or use 2 tins with 12 cups each.
Place biscuit mix, butter and sour cream in a large mixing bowl and stir with a wooden spoon until ingredients come together. Spoon batter by tablespoons into ungreased muffin tins, filling the cups 2/3 full.
Bake muffins on center rack of a preheated 350° oven until they are light brown, 15-18 minutes. Remove muffin tins from oven and place them on a wire rack to cool for 10 minutes. Then, run a sharp knife around edges of muffins and invert them onto the rack. Transfer to a platter and serve at once.