Sort, scrape, wash the mussels, discarding any that do not close. Steam them in a cup of water, in a large kettle. Drain mussels and reserve the cooking liquid. Remove the empty half shell from each mussel, and discard, leaving the mussel attached to other half shell.
In a food processor combine the ground almonds, pine nuts, crushed garlic, parsley, paprika, peppercorns and half of the oil. Mix to a thick paste.
In a medium pot, brown the onion in the remaining oil. Stir in the blended paste, and mix over a brisk fire, while stirring. Add the tomato paste and thin sauce with reserved mussel juice to obtain a thick sauce. Season to taste.
Loosen each mussel from the shell. Arrange on a serving dish. Fill each mussel with the sauce. Serve hot.