In 10" skillet heat 2 tbsp. butter over medium heat. Add bacon sliced and cut into 1/2" strips, cook 1 minute. Add sliced onions, cook 3 minutes, stirring frequently; remove from heat. In bowl beat eggs, grated cheese, pepper and bacon-onion mixture. In skillet melt butter over medium heat. Add egg mixture, reduce heat to medium-low, cook 10-15 minutes until bottom is set. Meanwhile, preheat broiler. Broil frittata until top is set and lightly browned, about 3 minutes.