Wash the potatoes, prick them with a fork, and place them on a sheet pan. Bake in a preheated 350 degree oven for 1 ½ to 2 hours, until they are very soft. Resist roasting them at a higher temperature; it will cause the skin and flesh just inside the skin to become crusty. Cool them slightly and scoop out the insides. Rice the scooped-out potato with a ricer or mash them with a fork. Place them in a bowl and cover with a damp cloth to retain their heat. The potatoes must be used while they are still very warm.
The gnocchi can be made up to 2 weeks in advance and frozen on sheet pans. Once they are frozen solid they an be transferred to a Ziploc bag or wrapped tightly. Do not thaw them before cooking or they will stick together. The sauce can be made in advance and stored for up to 1 week in the refrigerator or up to 6 months in the freezer.