Lemon Blueberry Icebox Cookies

Step 1
Place frozen blueberries in a microwave-safe bowl; microwave on High until defrosted, about 1 minute. Mash blueberries slightly with a fork; allow to cool, about 10 minutes.

Step 2
Whisk flour, baking powder, and salt together in a bowl; set aside.

Step 3
Beat sugar and butter with an electric mixer in a large bowl until smooth. Reduce speed to low; beat in flour mixture just until evenly dispersed; dough will be very crumbly. Press the mixture together with your hands until it forms a stiff dough; divide dough evenly between two bowls.

Step 4
Add lemon zest and lemon juice to one bowl; press dough firmly against the sides of the bowl with a spatula until zest and juice are fully incorporated.

Step 5
Add thawed blueberries and their juices to the second bowl. Again, press dough firmly against sides of the bowl with a spatula to mix until dough is uniformly purple. Both doughs will be somewhat sticky.

Step 6
Lay out a piece of parchment paper. Scoop out about 1 tablespoon lemon dough; place onto the parchment. Scoop out about 1 tablespoon blueberry dough and place it beside lemon dough, making sure doughs are touching. Scoop out another tablespoon of? lemon dough; place it, touching, directly behind blueberry dough. Scoop out another tablespoon of blueberry dough and place it, touching, behind lemon dough. Continue with remaining dough, alternating by tablespoons, until you have two rows of lemon and blueberry dough in a roughly rectangular checkerboard pattern on the parchment paper. With wet hands, press dough into a cylinder about 9 inches long and 1-1/2 inches in diameter. Roll dough in parchment paper, wrap in plastic wrap, and freeze at least 8 hours.

Step 7
Preheat the oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper or a silicone mat.

Step 8
Unwrap frozen dough; place on a cutting board. Slice dough into 12 cookies, about ¾-inch thick, with a sharp serrated knife; place cookies 2 inches apart on the prepared sheet.

Step 9
Bake in the preheated oven until cookies are lightly golden on the bottom, 15 to 17 minutes. Allow to cool on baking sheets for 5 minutes; remove to a wire rack to cool completely.