In a medium saucepan, combine fresh or frozen blueberries with lemon juice over medium heat. Stir gently as the mixture comes to a simmer, crushing the berries with a fork. Allow it to cook for 10-15 minutes until it thickens and resembles a jam. Remove from heat and let cool.

In a mixing bowl, whisk together granulated sugar and lemon zest. Add softened unsalted butter and cream together until light and fluffy, about 2-3 minutes.

Beat in one large egg and a splash of vanilla extract, then fold in the cooled blueberry reduction.

In a separate bowl, whisk together all-purpose flour, baking powder, and salt. Gradually incorporate this into the wet ingredients until just combined.

Cover the bowl with plastic wrap and refrigerate for at least 2 hours to chill.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Form dough balls about 1.5 inches in diameter, roll in granulated sugar, then coat generously in powdered sugar.

Place the sugar-coated dough balls on the prepared baking sheets, spaced about 2 inches apart. Bake for 10-12 minutes.

Let the cookies cool on baking sheets for about 5 minutes before transferring to a wire rack to cool completely.