01 - Heat a skillet over medium heat. Add unsalted butter and thinly sliced onion. Sprinkle with salt and cook, stirring occasionally, until softened and lightly golden, about 8 minutes. Remove from heat and set aside.
02 - While onions are cooking, heat the hot dog sausages using preferred method—grill, pan-fry, or simmer in hot water—until fully warmed, approximately 5 to 7 minutes.
03 - Lightly toast the hot dog buns if desired.
04 - Place one hot dog sausage into each bun.
05 - Arrange sautéed onions over each hot dog and drizzle with ketchup. Serve immediately while hot.