01 -
Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
02 -
In a small bowl, combine sugar and flour. Add cold, cubed butter and use a fork to mix until crumbly. Set aside.
03 -
In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy. Beat in egg and vanilla until combined.
04 -
In another bowl, whisk flour, baking powder, baking soda, and salt. Gradually add to wet mixture, mixing until just combined. Gently fold in blueberries.
05 -
Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them 2 inches apart. Slightly flatten each cookie.
06 -
Sprinkle streusel topping generously over each cookie.
07 -
Bake for 12-15 minutes, or until edges are golden. Cool on the baking sheet for 5 minutes before transferring to a wire rack.