From "Tapas" by Adrian Lissen. It's been a while since I've made these, but I recall that everyone loved these when we had a tapas party. Easiest if you make them the day before, then fry them right before serving.
Cook potatoes in boiling salted water until tender. Drain.
Put potatoes back in pan and heat over low flame until completely dry, stirring to prevent scorching.
Put potatoes in a food processor with the egg yolks, butter, salt and pepper. Pulse a few times.
Add the nutmeg, sherry, parmesan, mustard and parsley. Pulse until the consistency of very thick mashed potatoes. If the mixture is too wet or runny, put mixture in a large bowl and incorporate a bit of flour, working in with your hands.
Adjust seasoning, then form small cylinders (about 3 x 1 inches).
Roll croquettes in seasoned flour to cover, shaking off excess.
Dip in beaten egg mixture, then roll them in breadcrumbs. Set aside and repeat until all potato mixture is used up.
Deep fry at 375 degrees until golden brown, drain and keep warm until served.
NOTE: these can be prepared in advance thru step #7 and refrigerated in an airtight container. Bring to room temp before frying.