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

Cream the softened butter and granulated sugar for about 2–3 minutes, until light and fluffy.

Beat in the egg, vanilla extract, finely grated lemon zest, and 1–2 tablespoons of fresh lemon juice.

In a separate bowl, whisk together the all-purpose flour, baking powder, and fine salt. Gradually add the dry mixture to the butter mixture, mixing only until combined.

Gently fold in the fresh blueberries, taking care not to crush them. If using frozen blueberries, keep them frozen and fold them in carefully.

Scoop approximately 2 tablespoons of dough for each cookie onto the prepared baking sheets, leaving about 2 inches between portions. Chill the scooped dough for 30–60 minutes if it feels soft or sticky.

Bake for 10–13 minutes per batch, until the edges are lightly golden and the centers still look slightly soft.

Cool the cookies on the baking sheet for 5–10 minutes, then transfer them to a wire rack. For the optional glaze, whisk confectioners’ sugar with enough lemon juice to make a pourable icing and drizzle it over fully cooled cookies.