Grilled Beef and Onion Sandwich
- In a large saucepan, add red and white onions, honey, mustard, and vinegar.
- Over medium heat, stir and saute, until onions are crisp-tender, about 6 to 8 minutes.
- Butter 1 side of each slice of bread; top unbuttered side of each bread slice with 1/4 of the roast beef, 1 slice of cheese and 1/4 of the onion mixture.
- Top with remaining bread slices, buttered sides up.
- Heat a large skillet or griddle over medium heat.
- Place sandwiches in skillet.
- Cook, turning once, until cheese is melted and bread is toasted, about 2 to 3 minutes.