I was going to make Pierre Herme's lemon cream, and go the whole hog with 10.5 ounces butter. But I chickened out. I looked at other recipes and most of them are 1-2 ounces butter max for roughly the same amount.
This is a combination of the half a dozen recipes I have.
Zest of 2 lemons
3/8 cup lemon juice--1/4 and 2 tablespoons, or to make it easier, 90g
Prepare a bain-marie.
I rubbed the zest into the sugar, then poured the juice in before whisking in the eggs. Do this in a heatproof bowl, preferably stainless steel, because the next step is:
Set the bowl over the pot of boiling water and continue whisking until it is thick enough to coat a spoon.
Remove from heat and cool in a icebath--you could just leave it at room temperature, but it's quicker this way. Stir in the butter. Run through a sieve/chinois--this is important.
Bottle/Jar and store.
I run it through the sieve after adding the butter because it is easier--before that, it's too viscous, IMHO, but I plan to try that as well.
This freezes quite well (tastes like sorbet frozen), so you can make larger batches--this one makes a very small batch--if you have a big enough bowl and pot for the bainmarie.