Bring a small pot filled with an inch of water to a light simmer.
Separate 4 egg yolks and place each yolk into a medium-sized bowl that can fit into the simmering pot of water without touching the bottom.
Place your bowl on top of the simmering pot and add to your bowl your water, sugar, salt, and lemon juice.
Whisk together for 30 seconds, then take off of the heat.
Continue whisking until it becomes lighter in color.
Then, place it back on the heat and continue to whisk until the eggs thicken just a bit.
While continuously whisking, add in unsalted cold butter cut into cubes.
Add it in bit by bit, allowing them to melt into the mixture.
Continue this process until it’s fully emulsified. (If your sauce isn’t thick enough, whisk it over the heat for another 30 seconds).
Once done, pour sauce directly into a thermos - something to keep it hot.
Make sure to serve within one hour.
