Heat a sandwich maker or place a heavy-bottomed skillet over medium heat. Butter the slices of sourdough bread on one side each. Assemble the sandwich on the sandwich maker or skillet by placing one slice of bread buttered side down. Leave 1/4-inch of empty space around the outside edge of the bread and lay in half of the cheese topped with the hashbrowns, bacon, scrambled egg, and remaining cheese. Lay the second slice of bread -buttered side up- on the sandwich and close the sandwich maker. If using the skillet, use a fork to crimp the edges quickly and carefully. The sandwich maker will toast it evenly on both sides at the same time, making it unnecessary to flip it. If using the skillet, flip the sandwich after the first side is golden brown. Either way, transfer the sandwich to a plate when both sides are beautifully golden brown. Serve while still hot with hot sauce, if desired.