In a saucepan over medium heat, combine fresh or frozen blueberries with lemon juice. Allow the mixture to simmer gently for 10-15 minutes, stirring occasionally, until it thickens and reduces. Once done, remove from heat and let it cool completely before adding it to the cookie dough.

In a mixing bowl, combine granulated sugar with freshly grated lemon zest. Using your fingers, rub the mixture together until the sugar becomes fragrant and the oils from the zest are released.

In a large mixing bowl, add the softened unsalted butter to the lemon sugar. Using an electric mixer, beat the mixture on medium speed until it becomes fluffy and light in color, about 3-5 minutes.

Next, incorporate the egg, vanilla extract, and the cooled blueberry reduction into the butter-sugar mixture. Mix on low speed until well combined.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt until evenly blended. Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined.

Cover the mixing bowl with plastic wrap or a clean kitchen towel and refrigerate the dough for at least 2 hours, or up to overnight.

About 15 minutes before you’re ready to bake, preheat your oven to 350°F (175°C). Line your baking sheets with parchment paper.

Once the dough is chilled, scoop out tablespoon-sized balls of dough and roll them first in granulated sugar, followed by powdered sugar.

Place the sugar-coated dough balls on the prepared baking sheets, spacing them about 2 inches apart. Bake for 10-12 minutes until they’ve puffed up and have a cracked surface.

After baking, let the cookies cool on the baking sheet for about 5 minutes, then gently transfer them to a wire rack to cool completely.