01 - Preheat oven to 400°F.
02 - Trim crusts from bread slices and cut each slice diagonally into two triangles.
03 - Place bread triangles on a baking sheet and brush lightly with softened butter.
04 - Toast in the oven for 5 to 7 minutes, turning once, until golden and crisp. Remove and let cool.
05 - In a small bowl, mix cream cheese, horseradish, sour cream, Dijon mustard, lemon juice, salt, and pepper until smooth.
06 - Spread a thin layer of horseradish mixture over each toast point.
07 - Top each with a folded slice of roast beef.
08 - Garnish with chopped chives or parsley and additional black pepper if desired. Serve immediately.