Slice rolls in half and place bottoms on a baking sheet.
Mix together mayonnaise, ¼ cup Dijon and horseradish. Spread evenly over the cut side of the buns.
Top with the beef, cheese and caramelized onions. Put top back on buns.
Melt butter, the tablespoon of remaining Dijon, sugar and Worcestershire in a small saucepan or microwave. Spoon over the sandwiches, then sprinkle Everything Bagel seasoning on top.
Cover loosely with foil and put in oven at 350 for about 15 minutes. Remove foil and bake for another 10 minutes until brown and cheese has melted.