Place the blueberries, lemon juice and lemon zest in a saucepan and heat over medium heat until simmering.
Cook for 5-7 minutes, then strain pressing against the sides to get all the pulp out.
Add the blueberry mixture and sugar back to the saucepan and heat over medium low heat until the sugar has fully dissolved
Beat egg yolks.
Temper egg yolks then mix into the blueberry mixture fully.
Whisk in butter, one piece at a time until melted.
Cool at room temp for 30 minutes.
Store in jar in the fridge for 2 weeks.
Full recipe: wenthere8this.com/blueberry-curd