Heat the butter and sauté the filleted and diced trout with the onion. After a few minutes, deglaze with white wine and half of the trout stock and let it simmer for 10 minutes. Remove the trout meat and keep warm. Sauté in butter and cress until soft, pour the remaining trout stock and bring to a boil. Blend with a hand blender. Add egg yolks and whipped cream and season with salt and pepper. Spread the trout meat on the plates as a garnish for the soup.