Heat a large nonstick skillet or griddle over medium heat. Coat the skillet with cooking spray or brush with melted butter. Spoon 1/4 cup mounds of the batter onto the skillet, spreading with a spatula. Cook until the tops are covered with bubbles and the edges look cooked, about 2 minutes. Carefully flip the pancakes over and cook until the bottoms are lightly browned, about 1 minute. Repeat with the remaining batter. Keep the cooked pancakes warm in the oven on a baking sheet, if desired.