Instructions: To make soup: Peel onions; place them in an aluminum foil pouch with olive oil and season with a large pinch of salt. Seal onions in foil; place on a baking dish and bake in 300-degree oven for 2 1/2 hours, until very soft.

Meanwhile, remove green part of leek and discard, Chop white part and wash well. Melt tablespoon butter in a saucepan and saute leeks until very tender but not browned. Add stock and bring to a boil. Turn heat off, add whole tarragon to liquid, as well as saffron. Cover pot, and allow to steep to infuse flavor. After 30 minutes, remove tarragon from liquid. When onions are ready, place them in a blender with all the liquid that was released from onions inside the pouch. Add leek and saffron liquid to blender and blend to a fine puree.

(Caution: Be careful when pureeing hot liquids in a blender. It should be done with the pulse option.) Stop blender; season with salt and cayenne pepper to taste, add Pastis or Pernod and remaining butter. Blend until butter is incorporated. Pour soup back into a saucepan and reheat.

To serve, saute rock shrimp and divide among 6 bowls, garnish with chervil and chives. Divide soup among bowls. The soup can be made a day in advance.

If you would like to email yourself the recipe for later use, or share the recipe with your friends or family, enter the email addresses below and this recipe will be emailed to you and others as well.