In a medium heavy-bottom saucepan, combine blueberries, lemon juice, 1 tablespoon water, and 2 tablespoons sugar. Cook over medium heat until blueberries start to burst and are soft, 7 to 10 minutes.
Transfer mixture to the heatproof container of a blender, cover with lid, cover lid with a folded kitchen towel, and hold in place while blending blueberry mixture until smooth.
In a medium bowl, whisk together egg yolks, cornstarch, salt, and remaining 2 tablespoons sugar until smooth. Gradually add blueberry mixture to egg mixture, whisking constantly. Return mixture to pan. Cook over medium heat, stirring constantly, until mixture bubbles, thickens, coats a spoon, and registers 170° on an instant-read thermometer, approximately 5 minutes.
Strain mixture through a fine-mesh sieve into a medium heatproof bowl. Stir in butter, 1 cube at a time, until combined and smooth after each addition. Cover with a piece of plastic wrap, pressing wrap directly onto surface of curd to prevent a skin from forming. Let cool completely.
Transfer curd to an airtight container, refrigerate, and serve within a week.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/petite-lemon-pavlovas-with-blueberry-curd/