Step 1In a 2-quart heavy-bottom pot, melt the butter over medium heat. Add the green onions and sprinkle generously with salt. Cook, stirring often, until the onions are softened, about 5 to 7 minutes.
Step 2Stir in the peas, then the broth. Bring to a boil, reduce the heat and simmer until the peas are soft, 15 to 20 minutes. While the peas are cooking, mix the creme fraiche with the tarragon, parsley, chervil and chives in a small bowl; set aside.
Step 3When the peas are very soft, remove the pot from the heat and puree the contents with an immersion blender (or cool the mixture slightly, then transfer to a blender or food processor and puree until smooth). Press the puree through a coarse strainer into a large bowl. Thoroughly whisk in the herbed creme fraiche. Season with salt and pepper to taste. Chill before serving. (The soup is also great warm: Just add the herbed creme fraiche and reheat gently.)