Mushroom Sliders with Caramelized Onions
- Grill or broil portobello mushrooms and make Caramelized Onions. (Can be made a couple of days in advance.)
- Mix mayonnaise, mustard, and onion. (Can be covered and refrigerated a couple of days in advance.)
- When ready to serve, warm mushrooms, onions, and buns. Spread mayonnaise mixture on buns, top with mushrooms and onions and serve.