A beurre blanc is a classic French emulsified butter sauce, meaning 'white butter'. It starts with a reduction of shallots, white wine and sometimes vinegar, which is then enriched by whisking in cold butter piece by piece. The key to success is temperature control — the sauce must stay warm enough to melt the butter but not so hot that it splits. The butter should be added gradually in small cubes, each one fully incorporated before adding the next. This creates a smooth, glossy, creamy sauce that pairs beautifully with seafood. Using the cooking liquor from shellfish as your base adds tremendous depth of flavour to the finished sauce.