In a mixing bowl, combine flour, brown sugar, cold cubed butter, cinnamon, and salt to make the streusel. Mix until it resembles coarse crumbs and chill in the refrigerator.

Beat the softened butter, brown sugar, and granulated sugar with an electric mixer until fluffy. Add the egg and vanilla, mixing well.

Whisk flour, baking powder, and salt in a separate bowl. Gradually add this to the wet ingredients, mixing just until incorporated.

Gently fold in the blueberries with a spatula, making sure not to crush them.

Scoop portions of dough onto a lined baking sheet. Add blueberry jam on top and swirl it into the dough.

Sprinkle the chilled streusel topping over each cookie and press down lightly.

Preheat the oven to 375°F and bake for 12-15 minutes until golden brown.

Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.