Step 1

Heat the lime juice, sugar and zest in a saucepan over medium heat until the sugar is dissolved.

Step 2

Whisk the egg yolks in a medium sized bowl.

Step 3

Temper the egg yolks by pouring a VERY small amount of the warm lime liquid into the egg yolks while whisking. Keep adding small amounts until half the lime mixture has been incorporated into the egg yolks.

Step 4

Pour the egg yolk mixture back into the saucepan and whisk together.

Step 5

Continue to heat over medium heat. Add the butter, one piece at a time, whisking until melted. Continue adding the butter pieces, one at a time until melted, until it has all been incorporated. Be sure to whisk constantly while doing this.

Step 6

Continue whisking for about 5 minutes, or until the mixture has thickened and started to bubble a little.

Step 7

Remove from heat and let cool at room temperature. Pour into a jar and store in the fridge for up to 2 weeks.