Roast Beef and Brie Sliders

1 stick plus 3 Tbsp. butter, divided
2 onions, sliced
1/2 tsp. salt
2 Tbsp. brown sugar
1 Tbsp. Dijon mustard
1 Tbsp. honey
1 tsp. garlic powder
1/2 tsp. salt
1/4 tsp. freshly ground black pepper
12 pretzel or regular slider rolls
2 cups spinach
1 lb. deli-style roast beef
1 lb. brie cheese or Muenster, thinly sliced


Melt 3 tablespoons butter in a large skillet over low heat. Add onions and salt. Cook on low, stirring occasionally, until onions are soften and begin to caramelize, about 20 to 25 minutes. Add brown sugar and stir to combine. Cook for 5 to 10 minutes. Remove from heat; set aside.

Preheat oven 350º.

In a small saucepan, melt remaining butter over medium-low heat. Whisk in mustard, honey, garlic powder, salt and pepper. Cook for 1 to 2 minutes.

Brush a 9 x 13-inch baking dish with melted butter mixture. Place bottoms of rolls in dish. Layer spinach, roast beef and brie cheese on rolls. Top with caramelized onions. Place tops of the rolls on top. Brush remaining melted butter mixture on rolls and bake for 15 to 20 minutes covered with foil.