Set up a simple double boiler by boiling water in a vessel and placing a thick bowl on top of it.
Add the egg yolk and sugar into the bowl and mix until it forms a velvety smooth sauce.
Add the milk and cream to the egg mix and continuously mix until the mix starts to thicken.
Cook until it coats the back of the spoon and immediately take off the heat.
Add the yuzu extract and mix it well.
Remove from heat and cool in the refrigerator.
Add it on your cakes, pancakes, waffles, toast, and more!