Clean mussels. Cook them in 2 cups of boiling water, covered, for 8 minutes. Remove the mussel meat from the shells. Mince the onions, and mix with the crushed garlic. Heat the butter, add the onion and garlic and fry until golden brown. Lower the heat, add the mussel meat, salt, pepper and ketchup and fry for 7-8 minutes.

which case, you would only need approximately 2 lbs of frozen mussels.