Use carrot peeler to remove zest from lemons, careful to not include the pith.place zest and sugar in food processor, pulse till very fine. Cream butter, add sugar/lemon mixture. Add one egg at a time, then lemon juice and salt.
Over low heat, stir constantly until thickens. Around 10 minutes, just below a simmer. It will look like it is curdelling but when you continue stirring it turn very smooth.
Notes, Options, Substitutions
Lasts in the fridge about 6 days. Make sure to use fresh squeezed lemons as it makes a huge difference . The taste will blow your taste buds to the moon.