1. Clarify the butter: Slowly melt butter in a small saucepan over medium heat; skim off surface foam. Pour clear layer of butter into a large glass measuring cup, leaving behind the milky residue in the bottom of the pan, which can be discarded. Let butter cool until it is lukewarm.

2. Meanwhile, place egg yolks and wine in a heat-proof bowl set over a pan of simmering water. Whisk vigorously until mixture is very pale and whisk leaves a trail, 3 to 4 minutes. Remove bowl from heat; continue whisking until mixture is lukewarm, about 30 seconds.

3. Whisking constantly, add butter to the egg mixture a drop at a time at first and gradually increasing to a steady stream. When fully incorporated, stir in the water and lemon juice, and season with salt and cayenne pepper, if desired. Serve immediately, or keep warm over a pan of simmering water removed from heat.