50g (3 1/2 tbsp) unsalted butter (, cut into 1 cm / 1/2" cubes)
Pinch of salt
Instructions
Rub the sugar and zest together using your fingers in a small bowl (brings out lemon flavour).
Whisk – Put the lemon sugar in a small saucepan with the egg yolks and whisk to combine (use a small whisk). Add lemon juice, butter and salt, then mix. Place on the stove over medium heat (or medium low, if your stove is strong).
Thicken - Whisk every now and then as the butter is melting then constantly (but leisurely) once the butter is melted. When you see the first bubble (~3 to 4 minutes), whisk for 1 minute, then remove off the stove. It should have a custard like consistency - if not, keep cooking.
Cool – Pour into a small bowl (strain, if you see little egg lumps). Immediately cover with cling wrap touching the surface. Cool on the counter for 30 minutes then refrigerate for 1 hour before using.