Prick the potatoes all over with a fork and bake them in a 425 degree oven, directly on the rack for 40 minutes, or until tender when tested with a fork.
When the potatoes are done baking, peel off the skins, and rice them into a large bowl. Add the cheeses, eggs, and salt. Stir gently together. Add the flour, and as gently as possible, knead the dough into a ball.
Remove a golf ball sized piece of dough, and on a floured board, roll into a thin log, about a half inch thick. Cut the log into 3/4 inch pieces. I like to spread two logs worth of gnocchi pieces on a floured salad plate. Repeat with the rest of the gnocchi. You'll have about 6 to 8 platefuls when done.
Boil a large pot of salted water. Drop in one plateful of gnocchi at a time. Using a slotted spoon, remove the gnocchi as soon as they rise to the top. Drain them in a colander and then lay out flat to dry completely. Repeat until all the gnocchi are cooked.