Place egg yolks and eggs in bowl of standing mixer.
Place sugar and water in small saucepot. Place on low heat. During this time, begin to whisk the egg yolks on medium speed until it is pale and increased in volume (about 4-5 minutes). While the egg yolks are going, whisk the sugar in the saucepot until it has dissolved into a syrup. Then let sit over medium heat until it reaches 225-230 degrees.- If egg yolks finish early, just let the mixer continue going at the lowest speed until the sugar is ready.
Slowly stream the sugar into the egg yolks with the mixer running on speed 3 or so (low to medium). Once all sugar is added, bring up speed to high and mix until it is room temperature, about 10 minutes. Check the sides of the bowl- they should feel cool- or use a thermometer until it reaches about 70 degrees.
**During this time, make sure the butter is at room temperature as well (around 60-65 degrees).
Add butter in a few cubes at a time- no matter what, I’ve found that it often looks funky after I’ve added the butter, but if you just keep the mixture running at high speed for about 5-10 minutes, it evens out and incorporates.
Add in vanilla and citrus zest. Store in fridge until ready to use. It may need to sit out for about 20 minutes if it’s too cold/stiff.- If you have extra, you can freeze this and then defrost in the fridge for about a day beforehand.