Carp should be alive when you buy it. Ask fishman to bone carp, remove its skin, and cut meat into 4- or 5-inch chunks. Be sure he gives you the skin and bones. Also, make sure you purchase female carp with a lot of roe; purchase extra milt. If you buy a male fish with milt, purchase extra roe. Do not wash the inside of the fish; the blood makes the dish tasty.
Boil skin, bones and head of the carp in 2quarts water with 1teaspoon salt for about 20 minutes. Strain the broth.
Cook the onions in the fish broth for about 30 minutes. Force the onions through a sieve or purée in a blender and put back in the broth.
In a 4-quart soup or stew kettle place pieces of fish next to each other. Pour the onion broth over the fish. Add as much water as necessary to cover fish.
Bring liquid to a boil; add 1tablespoon salt, the paprika and green pepper. Cook for about 10 minutes. Do not stir, but shake the pot.
Add the roe and milt and cook for an additional 4 or 5 minutes. Let the soup stand for 5 minutes before serving.
Serve as a one-dish luncheon, or as a late-night supper dish, or for the soup and fish courses of a dinner.