Toad-in-a-Hole Sandwiches

Combine onion, 2 tablespoons butter, and ¼ teaspoon salt in a large cast-iron skillet. Cook over medium-high heat, stirring frequently, until light golden brown, about 20 minutes. Add 2 tablespoons butter, and reduce heat to medium-low; cook, stirring occasionally, until dark golden brown, about 25 minutes. Remove from skillet; wipe skillet clean.

Increase heat to medium-high. Add sausage to skillet; cook until browned, about 3 minutes per side. Remove sausage, and let drain on paper towels.

Reduce heat to medium-low, and melt 2 tablespoons butter. Add 4 bread slices; cook until golden brown, about 2 minutes per side. Set aside. Cut centers from remaining 4 bread slices with a 2½-inch round cutter.

Melt remaining 2 tablespoons butter in skillet. Place cut bread slices in skillet; cook until toasted, about 2 minutes. Turn, and crack 1 egg into each hole. Sprinkle eggs with pepper and remaining ½ teaspoon salt; cover and cook until whites are set, 2 to 3 minutes.

Place ¼ cup caramelized onions, sausage, and 1 slice cheese on each whole bread slice. Cover with bread slices with egg in hole. Top with hot sauce, if desired.