Remove skin and any nasty-looking pieces from calves' brains. Rinse in cold running water and pat dry with paper towels. Sprinkle with flour and season with salt and pepper to taste.

In a large skillet, heat oil over medium high heat. Add onion and saute until translucent. Add seasoned brains and brown slightly all over. Add vinegar and stock, reduce heat to low and let all simmer, covered, for 30 minutes.

Remove brains from skillet. Slice them and place slices in a 9x13 inch baking dish. Cook skillet juices rapidly to reduce. Meanwhile, preheat oven to 375 degrees F (190 degrees C).

Strain skillet liquid. In a small bowl beat egg yolks and mix will with the cream. Whisk mixture into skillet sauce. Pour sauce over brains and heat through in the preheated oven for 10 to 15 minutes.