TIP: If you have leftover beurre blanc that you want to save, pour it into a bowl and keep it in the fridge. Do not reheat it, or it will break into a greasy sauce. Instead, bring it back to room temperature, and when it's soft enough, whisk it over another bowl filled with hot tap water, until it's smooth. Then spoon over fish or scallops, or other vegetables, such as asparagus.