Separate eggs, putting whites in 1 large bowl and yolks in 4 separate small bowls. Whip whites until stiff peaks form. Fold in cheese, chives and bacon. Spoon into 4 mounds on parchment-lined baking sheet; make a deep well in center of each. Bake at 450 degrees for 3 minutes, then and 1 yolk to each well; season with pepper. Bake until yolks are just set, 2 to 3 minutes.