Thick, soft lemon cookies brightened with fresh zest and juice are crowned with a naturally colored blueberry cream cheese frosting made from freeze-dried blueberries for pure, vibrant flavor.
Make the cookies: In a medium bowl, whisk together the flour, cornstarch, baking soda, and salt; set aside.
In a large bowl using a handheld or stand mixer fitted with the paddle attachment, beat the butter, granulated sugar, and lemon zest on medium-high speed until creamy, about 3 minutes.
Add the egg, lemon juice, and vanilla; beat on medium-high speed until combined, about 1 minute. Scrape down the bowl and beat again as needed (mixture may look curdled).
Add the dry ingredients to the wet ingredients and mix on low speed just until combined. The dough will be thick and sticky.
Cover and chill the dough in the refrigerator for at least 2 hours and up to 3 days.
Preheat the oven to 350°F (177°C). Line baking sheets with parchment paper or silicone baking mats.
Bake cookies per recipe directions on the source page, then cool completely before frosting.
Make the blueberry frosting: Grind the freeze-dried blueberries to a fine powder and sift out any seeds. Beat the softened butter and cream cheese until smooth, then gradually mix in the confectioners’ sugar, lemon juice, vanilla, and a pinch of salt until creamy.
Frost the cooled cookies and, if desired, garnish with lemon slices and fresh blueberries.