Shallot, lemon, and tarragon are classic pairings for many dishes. I like to infuse their flavors into a vinegar and then make a sauce to use over fish. The sauce is light and bright, adding many base layers of flavor to the fish.
Preheat a water bath to 135°F (57.2°C).
Lightly scrub the outside of the lemon then remove the zest with a vegetable peeler. Make sure little to no pith came off as well, using a paring knife to remove any. Combine the lemon peel, tarragon, shallot, and vinegar in a sous vide bag or mason jar then seal and place in the water bath. Heat the infusion for 1 to 2 hours.
Prepare an ice bath with 1/2 ice and 1/2 water. Remove the bag or mason jar from the water bath and place in the ice bath for 15 to 20 minutes. Strain the vinegar and store in a sealed container.
Whisk together the infused vinegar and honey. Slowly whisk in the olive oil until fully emulsified. Salt and pepper to taste. Serve over warm, white fish.
I like to thicken this vinaigrette by blending in 0.15% xanthan gum. It also helps the vinaigrette cling to food when you use it.