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

Transform freeze-dried blueberries into a fine powder using a spice grinder or food processor.

In a large bowl, cream together the unsalted butter, granulated sugar, and light brown sugar for 2-3 minutes until fluffy.

Add the egg, vanilla extract, and lemon zest to the creamed mixture and blend until well combined.

Gradually mix in the all-purpose flour, baking powder, baking soda, and salt until just combined.

Divide the dough and mix in the blueberry powder into one half until fully combined.

Scoop out a ball of plain dough and one of blueberry dough, press together to create a swirl effect, and place on baking sheet.

Roll each dough ball in sugar, flatten slightly, and ensure there's enough space between each cookie.

Bake for about 8 minutes until edges are set and tops are lightly golden.

Allow cookies to cool on the tray for 5 minutes before transferring to a cooling rack.