Basic Butter Sauce

Put the shallots, water, and thyme in a small saucepan and bring to a boil over medium-high heat. Reduce the heat to medium and cook at a low boil until the shallots are very soft and the water has reduced to a generous 1/4 cup. Remove the thyme and turn the heat to very low. Use an immersion blender to start pureeing the shallots. Add a piece of butter and continue to puree, emulsifying the water and butter. Continue adding butter piece by piece, incorporating each bit of butter before adding another. Tilt the pan as you work and keep it over the heat. The sauce will become light and very pale yellow. Strain the sauce through a fine sieve, pushing down on any solids that remain with a wooden spoon. Return the sauce to the pan. Season with salt. Makes 1 cup. Your can serve the sauce right away or keep it warm at the back of the stove for an hour or so, giving it a whisk once in a while. Add a few drops of water if the sauce becomes too thick. Store any leftovers tightly covered in the refrigerator. To rejuvenate leftover sauce, put it in a saucepan over medium-low heat and bring to a simmer. The sauce will break (separate) at this point. Don't worry! Reduce the heat to low and re-emulsify the sauce with the immersion blender.