Heat a grill or cast-iron skillet to medium heat. Add sausages and cook until you get nice char marks and sausages are heated all the way through.

Melt butter in a pan over medium-high heat. Toast both sides of hot dog buns in melted butter, then sprinkle poppy seeds on outside of buns.

Assembly: place cooked sausages in buns, then drizzle with mustard. On either side of sausage, spread onions, tomato slices, relish, sport peppers, and pickle spears. Sprinkle celery salt on top and enjoy!