In a medium saucepan, combine fresh blueberries, ¼ cup of granulated sugar, and 1 tablespoon of fresh lemon juice over medium-low heat. Stir gently until thickened.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 tablespoon of cornstarch, 1 teaspoon of baking powder, and ½ teaspoon of kosher salt.

Using a stand mixer, beat ¾ cup of softened unsalted butter and 1¼ cups of granulated sugar together until light and fluffy, about 3 to 4 minutes.

Once fluffy, pour in 3 tablespoons of the cooled blueberry sauce. Mix on low speed until integrated.

Add in 1 large egg, 2 tablespoons of milk, and optional purple food dye. Mix until just combined.

Gradually fold the dry ingredients into the wet mixture until no dry bits remain.

Cover the bowl with plastic wrap and refrigerate the dough for at least 3 hours.

Preheat your oven to 325°F (163°C). Shape the chilled dough into balls and place them on parchment-lined baking sheets.

Bake for 15 minutes until the edges are set and cracks appear on top.

Allow the cookies to cool on the baking sheet for 10 minutes before transferring them to a wire rack.