This version of Beurre Blanc, the classic French white sauce, is more traditional in its use of shallots but forgoes vinegar for the aromatic and balanced tartness of Meyer lemon juice. We use Meyer lemon zest to finish the sauce at the end as well. If you cannot find Meyer lemons, then by all means substitute regular lemon juice—as long as it is fresh and not from a bottle. Tarragon is an herb that works particularly well with lemon and white wine, and we find that this simple sauce really elevates mild fish like sole, flounder or fluke.