Put the eggs in a pan with water to cover. Bring to a boil and cook for 10 minutes. Drain and cool in iced water
As soon as the eggs are cold, remove them from the water, shell them and set them aside until required
Put the minced beef and pork in a large bowl. Add the chopped shallot, nutmeg, thyme, parsley and egg. Mix thoroughly with clean hands until it holds together
Divide the meat mixture into four equal portions and knead each one around a hard-boiled egg to make an even coating of about 3/4-inch (2 cm) thick
Put the egg white and breadcrumbs in separate shallow dishes. Dip each covered egg in egg white, then roll in breadcrumbs until the outside is evenly and well coated
Melt the butter in the oil in a large frying pan over medium heat. Add the covered eggs an brown on all side but turning them with tongs
Reduce the heat, cover and cook for 30 minutes on low heat
Make the sauce by melting the butter in the oil. Add the chopped shallots or onion and saute for 3 minutes. Add the garlic and saute gently for 3 minutes more
Add the tomatoes and tomato paste. Simmer for 5 minutes, then add the sherry or Madeira and the bay leaf. Season and add the paprika. Cook over low heat for 20 minutes
Put the potatoes in a pan with lightly salted water to cover. Bring to a boil, reduce the heat and cook for 25 minutes, until tender. Drain the potatoes, return them to the pan and place over the heat to dry. Mash with the milk, butter, tomato puree and nutmeg
Pile the potato puree in the center of warm plates. Surround with most of the sauce. Cut the meatballs in half and arrange two on the sauce on each of the plates. Spoon the remaining sauce over. Garnish with the parsley and serve immediately