01 -
Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
02 -
In a large bowl, cream together softened butter and granulated sugar until the mixture is light and fluffy.
03 -
Add eggs one at a time, mixing well after each addition, then blend in vanilla extract.
04 -
In a separate bowl, whisk together flour, baking powder, baking soda, and salt until evenly blended.
05 -
Gradually add the dry ingredients to the butter mixture, mixing until just combined to avoid overworking the dough.
06 -
Gently fold blueberries and, if using, white chocolate chips into the dough using a spatula.
07 -
If preparing the streusel topping, combine brown sugar, flour, cinnamon, and cold butter, and cut together with a pastry blender or fork until crumbly.
08 -
Scoop dough onto prepared baking sheets, spacing evenly. Sprinkle streusel topping over each if using.
09 -
Bake in preheated oven for 10 to 12 minutes, or until the edges are lightly golden and the centers are just set.
10 -
Allow cookies to cool on baking sheets for several minutes before transferring to a wire rack to cool completely.