To make the gnocchi, prick the potatoes with a fork and put in the microwave and cook for 10 minutes, until soft and easily pierced with a knife. Let sit until cool enough to handle, then remove the skins.
Grate the potatoes on a box grater and transfer to a large bowl. Add the flour, salt, and egg.
Mix until the flour is incorporated and you have a soft dough. Cut in half and wrap one half with plastic wrap. Store in the refrigerator for later.
Cut the second half into 2 inch strips and roll into a cylinder. Cut into 1-inch pieces.
Bring a pot of salted water to boil. Add the gnocchi to the pot and cook until they start to float. Remove with a slotted spoon and transfer to a bowl.
To make the butter, put the butter in a large stainless steel skillet. Over medium low heat, cook until the butter is golden brown, and smells nutty. Add the sage leaves and cook for a minute. Remove.
Add the gnocchi to the pan and let cook until lightly browned. Add the lemon juice. Transfer to plates or bowls and add the cheese, sage leaves, and pepper.