To make beurre monte, bring 2 tbsp. water to a simmer in a small, heavy saucepan over medium heat. Reduce heat to medium-low, and gradually whisk in anywhere from 1 tbsp. to 1 lb. unsalted butter, 1 tbsp. at a time, until water and butter have emulsified. Keep temperature between 180°-190° (if the mixture boils, it will separate). Use beurre monte immediately, or keep it warm in a pan set over a pot of simmering water over medium-low heat. Refrigerate any leftover beurre monte, and use as you would regular butter.