In a large bowl, cream softened butter with brown and granulated sugars until light and fluffy
Beat in the egg, then stir in vanilla extract
In a separate bowl, whisk together flour and baking powder
Gradually add the flour mixture to the butter mixture, mixing until just combined. Do not overmix
Gently fold in blueberries (tossed with 2 tablespoons flour) to prevent sinking
Drop rounded tablespoons of dough onto a lined baking sheet, spacing 2 inches apart
Bake for 13-15 minutes, until golden around the edges but still soft in the center
Cool on the baking sheet for 10 minutes, then transfer to a wire rack
Notes
Toss blueberries in flour before folding into dough to improve texture and prevent sinking
Use frozen berries (thawed and patted dry) for off-season baking
Store in an airtight container for up to 5 days