1. Bring the water to a boil and add 1/2 tsp salt.
2. Boil the edamame until beans are tender, 4 to 5 minutes.
3. Dissolve the arrowroot in 1 tablespoon of the chicken broth to make a paste. Bring the remaining broth to a boil.
4. Stir the paste into the broth and allow the broth to thicken slightly. Remove from the heat and add the vinegar, mustard, 1/4 tsp salt, pepper, tarragon, shallot, and garlic.
5. Whisk in the olive oil. Makes 1/4 cup dipping sauce.
Serve with Salmon and Wild-Rice Stuffed Cabbage.