Peel asparagus stalks, set aside tips, and chop remaining stalks into 1cm pieces.
Melt butter in a saucepan and sweat the shallot for 5 minutes without browning.
Add chopped stalks and sweat gently for another 5 minutes.
Pour in stock and simmer for 20-30 minutes until stalks are very tender.
Process the mixture in a food processor until smooth and return to the saucepan.
Return to a simmer, add reserved tips, and cook for 5 minutes.
Stir combined crème fraîche, egg yolks, and sherry into the soup off the heat.
Thicken the soup over very gentle heat while stirring constantly.
Garnish with parsley and serve with buttered bread.