In a medium saucepan, combine blueberries, fresh lemon juice, and lemon zest. Heat over medium heat for 5-7 minutes until blueberries soften and burst.

Pour the mixture through a fine sieve into a bowl, pressing down to extract as much juice as possible.

Return the strained blueberry juice to the saucepan, add granulated sugar, and stir until dissolved over medium heat for 2-3 minutes.

Whisk together egg yolks in a separate bowl. Gradually add half a cup of warm blueberry mixture to egg yolks while whisking.

Pour the tempered egg mixture back into the saucepan with the blueberry juice and cook over medium-low heat, stirring until thickened.

Reduce heat to low and whisk in unsalted butter, one tablespoon at a time, until completely melted.

Pour the Blueberry Curd into a heatproof bowl, cover with plastic wrap, and let cool at room temperature for 30 minutes.

Transfer cooled curd to an airtight container and refrigerate for up to 2 weeks.