Wash potatoes and place on 2 lightly oiled cookie sheets. Bake for about 30 minutes.
Cool potatoes before handling.
Trim either end of each potato and then cut in half, leaving trimmed edges on the end to allow potatoes to sit upright. Using a small melon baller, scoop out inside of each potato half, leaving at least 1/8-inch edge.
Fill pastry bag, fitted with a star tip, with creme fraiche. Fill each scooped-out potato half with piped creme fraiche.
Garnish top of each potato with red or black lumpfish roe.