Lightly spoon flours into dry measuring cups; level with a knife. Combine all-purpose flour, whole wheat flour, yellow cornmeal, baking powder, and garlic salt in a food processor; pulse 3 times or until combined. Add 1/2 cup water, butter, and egg; pulse 3 times or just until combined (do not form a ball). Place the dough on a lightly floured surface; knead gently 4 to 5 times. Divide the dough into 12 equal portions. Roll each dough portion into a 5 1/2-inch circle on a lightly floured surface. Stack the dough circles between single layers of wax paper or plastic wrap to prevent sticking; chill the dough until ready to use.