Preheat the oven to 400°F. Line two baking sheets with parchment paper or silicone baking mats.
Slice the baguettes on a slight angle into ¼-inch thick slices. Brush both sides of each slice with olive oil. Sprinkle each side lightly with salt and pepper. Bake in the oven for 10-15 minutes or until golden brown and crunchy.
Can be made ahead – let cool completely, then store without toppings in an airtight container for up to 3 days.
Combine the sour cream and horseradish.
Top the crostini with a slice of beef. Dollop some of the sour cream horseradish sauce on top and sprinkle with chopped chives.
The sour cream horseradish sauce can be made up to three days ahead and stored, covered, in the refrigerator. Once assembled, the crostini are best served immediately.