FOR CARAMELIZED ONIONS
2 tbsp. extra-virgin olive oil
1 large onion, halved and thinly sliced
FOR POPPY-BUTTER TOPPING
4 tbsp. melted butter
1 tbsp. poppy seeds
2 cloves garlic, minced
1/2 tsp. Worcestershire sauce
12 mini Hawaiian rolls
1/4 c. mayonnaise
1/4 c. honey mustard
2 lb. deli sliced ham
1 lb. sliced Swiss cheese
Make caramelized onions: In a large skillet over medium, heat oil. Add onions and season with salt. Reduce heat to medium-low and cook, stirring occasionally until onions are caramelized and jammy, about 25 minutes. Let cool slightly.
Preheat oven to 350°. Make poppy butter topping: In a medium bowl, combine butter, poppy seeds, garlic, and Worcestershire.
Make sliders: Split slider buns in half horizontally and place bottom halves on baking sheet. Spread mayo in an even layer on bottom layer of slider buns, then top with half the ham. Top with Swiss, then remaining ham.
Spread ham with honey mustard and onions and close sandwiches. Brush poppyseed dressing on tops of buns until all buns are coated.
Bake until cheese is melty and buns are golden, 10 to 12 minutes.