How to Make It
Preheat oven to 425°F. Starting at 1 end, slice each potato crosswise in 1/10-inch intervals, cutting most, but not all, of the way through each potato. Place potatoes in a bowl. Drizzle with 2 teaspoons olive oil; toss gently to coat. Arrange potatoes on an aluminum foil–lined baking sheet. Bake in preheated oven until potato slices begin to fan open, about 20 minutes.
Remove baking sheet from oven, leaving oven on. Gently pry apart potato slices to fan them open more. Brush remaining 4 teaspoons oil over tops of potatoes, making sure to get oil in between slices. Bake until tender and lightly browned, 25 to 30 minutes. Sprinkle evenly with salt. Cool slightly, about 5 minutes. (If potatoes are too hot, the crème fraîche will melt when applied.)
Top each potato with 1/2 teaspoon crème fraîche and 1/4 teaspoon caviar, alternating black and red caviar for effect, if desired.