Peel the cooked potatoes and press them through a potato ricer.
Spread the mixture on a work surface and knead with flour, semolina, egg yolks, salt, a little nutmeg and pepper to form a soft but malleable dough. Let rest in a cool place for about 60 minutes.
In a large pot, bring enough salted water to a boil and cook a test gnocco first. If the dough is too soft, add some more flour or semolina.
Then form a dough roll as thick as your thumb. Cut off pieces of dough about 3 cm long, shape them into rounds and press them in lengthwise with a fork.
Put the gnocchi into the boiling water, let them rise and steep for another 2-3 minutes. Carefully lift out and drain.