The whole dish can actually be made in about 10 minutes if you don't choose to clarify the butter the way I've done here.
Mix browned butter and butter in a pot and melt it. You can easily omit the browned butter; I just think browned butter pairs very well with white asparagus.
When the butter is melted, pour it into a bag and seal it. Hang the bag in a cold place (outside if it's cold enough, or in the fridge), but make sure the bag hangs at an angle. Once the butter has solidified, the whey will settle at the bottom of the bag, and you can easily separate the whey from the now clarified butter. You can, for example, cut a hole in the bottom of the bag so the whey drains out without you having to separate it manually.
Melt the butter again, either in the microwave or in a pot. It's important that it doesn't get too hot, as it should be around 40-50 degrees Celsius (104-122 degrees Fahrenheit) when making the sauce. If you melt it in the microwave, take it out when there's still one-third left unmelted, so the remaining butter melts from the heat of the already melted butter and retains a good temperature.Pour the butter into a small jug.
Warm the lemon juice and egg yolks in a thick-bottomed pot over very low heat. Whisk them together well. It should start to foam, and a good rule of thumb is that you should be able to touch the sides of the pot without it being uncomfortable, then it's not too hot. Remove from the heat if it gets too hot and continue whisking off the heat for a bit.
Add a little butter to the pot while whisking quickly.
Continue with a bit more butter and keep adding more butter gradually.
When you've used up all the butter (or perhaps a little before), the sauce has thickened and should be seasoned with salt and (white) pepper.
Serve immediately.