For the sauce, let the butter melt in a saucepan. Add the white wine and simmer for 1 to 2 minutes. Then add the cream and bring to the boil again. Stir the egg yolks into the sauce and season with salt, pepper, lemon juice and the mustard.
Wash the fish and pat dry. Rub lemon juice on both sides and season with salt and pepper. Mix the eggs in a soup plate. Place the flour and breadcrumbs each on a separate plate. First turn the fillets in the flour, knock off excess flour, then pull through the egg. Then turn the fillets in breadcrumbs. Make sure that the fillets are completely covered with flour, egg and breadcrumbs during each of the 3 steps.
Melt the butter and brown butter together in a pan and fry the fillets until golden brown on both sides.