Prepare the Streusel: In a medium bowl, combine flour, brown sugar, cold butter, cinnamon, and a pinch of salt until resembling coarse crumbs. Refrigerate while making the dough.

Make Cookie Dough: Beat softened butter with brown and granulated sugars until fluffy. Add egg and vanilla, mixing well.

Combine Dry Ingredients: Whisk together flour, baking powder, and salt. Gradually incorporate into wet ingredients.

Incorporate Blueberries: Gently fold in fresh blueberries to maintain their shape.

Assemble Cookies: Portion dough onto a baking sheet and dollop blueberry jam on each mound, swirling slightly.

Top with Streusel: Sprinkle chilled streusel over cookie dough and press lightly to adhere.

Bake: Preheat oven to 375°F and bake for 12-15 minutes until edges are set.

Cool: Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.