Step 1Place potatoes in pot, cover by 2 inches with cold water and bring to a boil. Reduce heat to simmer and cook until tender, about 25 minutes. Drain.
Step 2While still warm, peel potatoes and pass them through tamis. Weigh out 9 ounces of resulting puree (about 1 3/4 cups, packed). Working quickly, whisk flour into potatoes, then whisk in creme frai^che. Add 1 egg, whisking batter until smooth. Add second egg, and then yolk, whisking until smooth. Batter should fall from whisk in thick stream but hold its shape. Add a little more creme frai^che if batter is too thick. Season with salt and pepper to taste.
Step 3Heat nonstick pan over medium-low heat. Spoon 1/2 tablespoon of batter into skillet for small blini, more for larger blini as desired. Cook 2 minutes, flip and continue cooking another minute or until done. Blini should be golden brown. Keep warm while you make successive batches.
Step 4Serve immediately, topped each with a dollop of caviar.