Top one of the slices of sourdough with one 1 ounce slice of provolone, then top with 2-3 tablespoons of leftover mashed potatoes, evenly smoothing them over the provolone.
4 pieces sourdough bread, 2 slices of provolone, 4-6 tablespoons mashed potatoes
Top with 2 pieces of crumbled bacon, 1 teaspoon chopped scallions, ¼ cup cheddar, and some black pepper.
4 pieces bacon, 2 teaspoons scallions, ½ cup cheddar, black pepper
Repeat with remaining sandwich.
In a large skillet, melt butter over medium heat. Add grilled cheeses, pressing down lightly, and cook for 3-5 minutes until golden. Flip and continue cooking until cheese is melted and bottom piece is golden. Serve immediately, with additional black pepper and scallions.
2 tablespoons butter