Preheat the oven to 350℉. Line a baking sheet with parchement paper and set aside.
Cream butter, granulated sugar and brown sugar together until light and creamy. Add the egg, vanilla extract and mix until smooth.
Mix in flour, corn starch, baking powder, baking soda and salt.
Fold in the blueberries (don’t over mix).
Drop small dollops of jam onto the dough and swirl with a skewer to make streaks of jam in the dough.
Scoop out 8 equally sized dough balls (using an ice cream scoop) onto the baking sheet, and top with the streusel.
Bake for 13-14 minutes and allow to cool on the baking sheet for 15-20 minutes.