Soak brains in cold water and peel off membrane. Drop brains into boiling water for 1 minute, then remove. Dry and scrape with a knife, reducing the calf's brains to a rough pulp.
Cook onion in butter over low heat for about 10 minutes. Add pepper, paprika, and brains to the onion and continue to cook, covered, over very low heat for about 10 minutes.
Beat eggs as for scrambling. Just before serving, add the lightly beaten eggs to the calf's brain mixture. Be sure to mix brains and eggs thoroughly. The texture should be creamy, not hard scrambled eggs. Add salt to taste.