Preheat oven to 400.° Slice the baguette on the diagonal into 36 slices. Place onto an ungreased baking sheet and spritz with cooking spray. Sprinkle with a little fresh ground pepper. Bake until lightly browned, 4-6 minutes.
While the crostini is toasting – in a small bowl, combine sour cream, chives, horseradish and salt.
Top each crostini with a thin layer of the sour cream mixture, a slice of roast beef – then a pretty dollop of the sour cream mixture. Sprinkle with bleu cheese, then artfully place a single long chive diagonally across each crostini.
Place on a delicate, white serving platter and enjoy!