1-4 tablespoons unsalted butter
Place butter in a microwave-safe bowl. Cover and microwave on medium power until melted, 30 seconds to 1 minute.
Add half-and-half, egg yolks, lemon juice, salt, and cayenne pepper to melted butter; stir to combine.
Microwave, uncovered, on medium power for 2 ½ minutes. Stir, and microwave on medium power for 1 more minute.
Remove from the microwave and whisk until fluffy; sauce may look curdled at first, but it will become nice and smooth as you whisk it.