Step 1

Melt 3 tablespoons butter in a soup pot over medium heat. Add the green onions or ramps and turn the heat to medium-low. Cover the pot and cook gently for 10 minutes.

Step 2

While the onions are cooking, pour the stock into another pot and bring to a simmer.

Step 3

Turn the heat up, add the sorrel leaves and a healthy pinch of salt to the pot with the onions and stir well. When the sorrel is mostly wilted, turn the heat back to medium-low, cover and cook 10 minutes. Stir occasionally. Mix in the flour and cook over medium heat for 3 minutes.

Step 4

Whisk in the hot stock, stirring constantly. Bring this to a simmer.

Step 5

To finish the soup, whisk together the egg yolks and cream. Temper the mixture by ladling a little soup into it with one hand, while you whisk the egg-cream mix with the other. Repeat this three times. (You are doing this to prevent the eggs from scrambling) Now start whisking the soup. Pour the hot egg-cream-soup mixture into the pot with the soup, whisking all the way. Add the final tablespoon of butter. Let this cook -- below a simmer -- for 5 minutes. Do not let it boil or the soup will break. Serve at once.