01 - Preheat oven to 350°F. Line a baking sheet with parchment paper.
02 - In a small bowl, whisk together mayonnaise, Dijon mustard, and horseradish if using until well combined.
03 - Slice slider buns horizontally. Arrange bottom halves on the prepared baking sheet.
04 - Spread sauce evenly over bottom bun halves.
05 - Top each bun with corned beef, drained sauerkraut, and a slice of Swiss cheese.
06 - Place top bun halves over cheese layer to form sandwiches.
07 - Brush bun tops with melted butter. Sprinkle with caraway seeds and black pepper if desired.
08 - Cover loosely with aluminum foil. Bake for 10 minutes.
09 - Remove foil and continue baking 5 minutes until cheese melts and tops turn golden brown.
10 - Serve sliders immediately while warm.