In a small saucepan, combine salsify, 1 tablespoon cream, and 1 cup water. Bring to a boil, reduce heat, and simmer until tender, about 20 minutes. Remove from heat and cool completely. Store salsify in liquid until ready to use.
To open oysters, place a clean kitchen towel on a cutting board. Arrange towel so that it allows an oyster to sit level, with flat shell facing upward. Pry the shells apart by forcing your oyster knife into the narrowest part of the shell. Be sure to reserve all of the juices. Sever the abductor muscle and reserve. Strain juices.
In a small skillet, combine leek and 3 tablespoons water. Gently cook until leeks are tender and juices have concentrated, about 15 minutes.
In a medium saucepan, combine reserved oyster liquid, abductor muscles, wine, clam juice, fumet, shallot, thyme, and bay leaf. Bring to a boil, reduce heat, and simmer until reduced by one-half. Add remaining 1/4 cup cream and return to a boil. Whisk in butter until just melted. Strain. Transfer to skillet with leeks. Add oysters, and bring to a simmer until oysters plump slightly, about 30 seconds. Spoon oysters into warm soup plates. Sprinkle with chives and chervil. Serve immediately.