In a small saucepan over medium heat, add the blueberries and cook for 5–7 minutes, stirring often, until the berries burst and become jammy. Remove from heat and cool slightly, then blend or mash until smooth, yielding about ½ cup of puree.

In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy—about 2–3 minutes.

Beat in the large egg and one teaspoon of vanilla extract along with the cooled blueberry puree.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry mixture to the wet ingredients, mixing just until combined.

Cover the bowl with plastic wrap and chill the dough for at least 1 hour.

Preheat your oven to 350°F (175°C).

Scoop about 1½ tablespoons of dough and roll it into a ball. Generously roll each dough ball in powdered sugar, coating all sides.

Place the coated dough balls on a parchment-lined baking sheet, spacing them about 2 inches apart.

Bake for 10–12 minutes, or until the cookies have spread slightly and developed a crinkly top. The centers should look soft but not wet.

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