Preheat oven to 375℉. Line a baking sheet with parchment paper.
Measure out one cup of the blueberries, mash with a fork, and set aside.
Beat butter and sugar until light and fluffy.
Add egg and mashed blueberries and mix until combined.
Add flour, baking powder, and salt and mix until almost incorporated.
Add remaining two cups of blueberries, and mix just enough to evenly disburse.
Scoop 1-2 tablespoon balls of dough and place on lined baking sheet.
Bake for 12-15 minutes, until the bottom edges are golden brown.
Cool on the baking sheet completely. Enjoy!
Notes
Be cautious when mashing the blueberries as the juices may splatted and stain.Mix the batter as little as possible after the whole blueberries are added to avoid smushing them.While the batter will have a purple hue, the color bakes out so if you're looking for a colorful cookie, add a few drops of food coloring.