Cream together the butter and sugar, add the eggs add egg yolk and cream everything together well. Add the Lemon juice and zest and whisk it all together, don�t panic if the mixture curdles, it will all work out at the end!
Pour the mixture in a saucepan and cook on medium low heat for about 10 minutes stirring constantly with a wooden spoon.
The curd will be done when it thickens and coats the back of the wooden spoon. Pour the mixture in a bowl, cover with plastic wrap (make sure the plastic is touching the curd so it prevents a skin from forming).
Allow to cool completely in the fridge before serving.
