10 large egg yolks
1 cup plus 2 tbsp sugar
1 stick unsalted butter, softened
Zest the lemons, set aside the zest then cut the lemons in half and juice them. There should be around 2/3 cup of lemon juice.
In a large heatproof bowl, whisk the egg yolks, sugar, lemon juice and zest. Place over a saucepan of simmering water, cook the curd and stir often until it thickens and reaches 185 degrees, will take about 10 minutes.
Strain the mixture through a sieve into a medium bowl. Gradually whisk in the butter a tablespoon at a time. Press a piece of cling film directly over the curd, pierce a few holes in it to allow steam to escape and leave to cool. Once the curd has cooled transfer it to a covered container and refrigerate.