2) With a mandoline or other manual slicer, cut the potatoes crosswise into thin slices. Arrange the slices in one layer on a baking sheet and brush with some of the remaining oil. Sprinkle the potatoes with rosemary, salt and pepper. Repeat for the remaining two baking sheets.
3) Bake the potato slices in the middle of the oven until golden, 15-20 minutes. With a metal spatula, immediately transfer the crisps to a rack to cool completely.
Top each of the potato crisps with 1 teaspoon of the creme fraiche and then the caviar. Serve immediately.