In the steel bowl of your stand mixer or using a hand mixer cream the butter and sugar together for 2-3 minutes. Add one egg at a time and mix.
Add the lemon juice, corn starch, lemon zest and put the mixture in a saucepan over medium heat. Stir continuously, the mixture will thicken in 8-10 minutes.
Switch off the flame and remove the saucepan from heat. Lemon curd should coat the back of your spoon when done.
Strain the mixture, cover and let cool to room temperature.
Lemon curd should stay fresh in the fridge for a week.