Step 1Bring a large pot of water to a boil over medium-high heat, adding 1 tablespoon of salt per quart of water. Slice the turnips and radishes in half if large; leave the smaller ones whole.
Step 2Blanch the turnips, radishes and carrots for 5 minutes, less if smaller, then lift them out of the simmering water and plunge them into an ice water bath. Drain, pat dry and set aside.
Step 3Bring the water back to a boil and add the fava beans; blanch 1 minute. Remove with a slotted spoon and place in the ice water bath. Reserve the cooking water. Pop the fava beans out of their skins and reserve the beans.
Step 4Melt 1 tablespoon of the butter in a 10-inch saute pan. Add the green onions and cook over medium heat for about 2 minutes, stirring frequently. Add one-half cup of the vegetable cooking water, the blanched vegetables, half of the parsley and tarragon and one-fourth teaspoon salt. Simmer until the vegetables are fully tender, about 10 minutes or until done. Add one-fourth cup cooking water as needed to maintain a small amount of sauce in the pan.
Step 5Add the fava beans, remaining butter and lemon juice. Increase the heat and swirl the pan back and forth until the butter has melted. Remove from the heat, add the rest of the parsley and tarragon, season with salt and pepper to taste and serve.