Place sauce pan on your kitchen scale. Add 6 egg yolks and 300g sugar to a saucepan and whisk together until combined.
Pour in 100g bottled lemon juice and whisk again.
Place over medium heat and stir with a wooden spatula constantly, scraping the bottom and corners of the pan, until it just comes to a simmer.
As soon as it simmers, take it off the heat and drop in 50g butter. Stir until fully melted.
Keep whisking until the curd thickens to a spoonable consistency.
Pour straight into a jar and leave to cool before putting the lid on and transferring to the fridge.
