Beurre blanc is the iconic butter-based fish sauce from Nantes. In fact, if you strain out the shallots, it is beurre nantais. Think of it as a hollandaise without the egg. The sauce uses one of the few wines grown in the region - muscadet, which comes from the melon blanc grape. Infinite variations are possible by using a different white wine, adding spices, steeping it with other flavors, or varying the liquids.