Makes 3 dozen

[ingredients]1 tablespoon unsalted butter
1 tablespoon olive oil
4 large Vidalia onions ( about 3 pounds), cut into 1/2-inch dice
4 tablespoons prepared horseradish
8 ounces cream cheese, room temperature
Coarse salt and freshly ground pepper
18 thin slices wheat bread
8 ounces roast beef, thinly sliced

[instructions]
1. In a large skillet, heat butter and oil over medium heat. Add onions, and stir to coat; cook, stirring occasionally, until they begin to soften, about 10 minutes. Reduce heat to medium-low; continue cooking, stirring every 20 minutes, until onions are amber colored and completely carmelized, just over 1 hour. Remove from heat, and transfer to a bowl to cool.
2. In a small bowl, mix horseradish and cream cheese; season with salt and pepper. Spread two slices of bread with onions and roast beef, and top with the second bread slice. Use a serrated knife to trim crusts, and cut into four small squares. Repeat with remaining ingredients. Cover with damp paper towels until ready to serve.