Ham and Swiss Sliders

Directions

1. Without separating the rolls, cut rolls in half horizontally. Arrange bottom halves of rolls in a greased 9x9-in. baking pan. Spread cut side of roll bottoms with horseradish sauce. Layer with ham and cheese; place top half of the rolls.
2. In a small skillet, heat butter over medium-high heat. Add onion; cook and stir until tender, 1-2 minutes. Stir in remaining ingredients. Pour over rolls. Refrigerate, covered, for several hours or overnight.
3. Preheat oven to 350°. Remove rolls from refrigerator 30 minutes before baking. Bake, covered, 25 minutes. Bake, uncovered, until golden brown, 5-10 minutes longer.