Mix the streusel ingredients with a fork until crumbly. Set aside.
Preheat oven to 350°F. Line a baking sheet with parchment.
Cream butter + sugars until light. Add egg + vanilla. Mix until smooth.
Add dry ingredients. Mix until just combined.
Fold in blueberries gently. Swirl in jam (don’t overdo it!).
Scoop 8 dough balls, top with streusel.
Bake 13–14 min. Let cool 15–20 min. Enjoy carefully—these are soft!
