How to Make It
In a bowl, beat the eggs with the yolk. Stir in the cheese, bread crumbs, lemon zest, nutmeg and butter. Cover the dough; chill until firm. Bring the dough to room temperature before cooking.
In a large saucepan, bring the stock to a boil. Season with salt and reduce the heat so the stock simmers.
Press one-third of the passatelli dough at a time through a ricer, cutting it in 1/2-inch lengths over the soup. Simmer until all of the passatelli surface, about 1 minute. Serve the soup in wide bowls.