Step 1

Make the sauce: in a small bowl, combine melted butter, honey mustard, and sweet pickle relish together. (Note: if honey mustard or relish is cold, you may need to re-melt the butter mixture once combined.) Stir in the poppy seeds and chopped onion.

Step 2

Layer the Swiss cheese and butter mixture on the buns, cutting the cheese slices to match the size of bun if needed.

Step 3

Wrap each sandwich in foil. Heat in oven at 350°F. until cheese melts, about 15 minutes. Serve hot!