Preheat the oven to 400°F, with a rack in the center., Work the cold butter into the baking mix, leaving some butter in small, visible pieces., Whisk the eggs and milk together., Stir the wet ingredients into the dry mixture., Lightly dust your work surface with baking mix, and turn the dough out onto it., Fold the dough over on itself four times, then gently flatten it to about 3/4" thick. Brush any surplus baking mix off the top of the dough. Cut with a 2 1/2" round cutter dipped in baking mix., Stack the scraps together, gently pat down to 3/4" thick, and cut additional biscuits., Set the biscuits 2" apart on an ungreased or parchment-lined pan. Brush with milk or melted butter, if desired; this will help the biscuits brown., Bake the biscuits for 14 to 18 minutes, until they're golden brown. Remove them from the oven and let them rest for 10 minutes or so before serving; they're best enjoyed slightly warm.