Make the Streusel: Combine ½ cup flour, ½ cup brown sugar, ¼ cup cold butter, ½ teaspoon cinnamon, and a pinch of salt. Mix to resemble coarse crumbs and chill.

Prepare the Cookie Dough: Beat ½ cup softened butter, ½ cup brown sugar, and ¼ cup granulated sugar until fluffy. Add 1 egg and 1 teaspoon vanilla extract, mixing until creamy.

Combine Dry Ingredients: Whisk together 1½ cups all-purpose flour, 1 teaspoon baking powder, and ½ teaspoon salt. Gradually add to wet ingredients until just combined.

Fold in Blueberries: Gently incorporate 1 cup of fresh blueberries without breaking them.

Portion the Dough: Drop rounded mounds of dough onto a parchment-lined baking sheet, dollop ½ teaspoon of blueberry jam on each.

Add Streusel: Remove chilled streusel and sprinkle it over each cookie mound, pressing down gently.

Bake: Preheat oven to 375°F (190°C) and bake for 12-15 minutes until edges are golden brown.

Cool: Let cookies cool on the baking sheet for 5 minutes then transfer them to a wire rack.