Stir olive oil and 1 clove grated garlic together in a bowl. Brush onto the crostini.
Bake crostini until golden, about 5 minutes. Set aside.
While crostini are toasting, make the horseradish sauce. Combine the crème fraîche, horseradish, Dijon, remaining clove of grated garlic, salt, and pepper in a bowl.
Tear the roast beef into 1-inch wide strips and roll to fit onto crostini. Top each crostini with a piece of beef.
Add a dollop of horseradish cream onto the tops of the roast beef rolls.