Whisk the egg yolks, lemon juice, and maple syrup together in a stainless steel bowl (or any bowl that you won't melt when you put it on top of a hot saucepan) until the mixture is thickened and doubled in volume.
Place the bowl over a saucepan containing barely simmering water (or use a double boiler). The water should not touch the bottom of the bowl.
Continue to whisk rapidly. Slowly drizzle in the melted butter and continue to whisk until the sauce is thickened and doubled in volume. Be careful to not let the eggs get too hot or they will scramble.
Remove from heat, cover, and place in a warm spot until ready to use.
If the sauce gets too thick, whisk in a few drops of warm water before serving.
Hollandaise sauce should not be made in advance. For best results, it should be served within one hour of preparing it.