Preheat oven to 350°F (175°C). Grease or line a 9-inch round cake pan with parchment.
Whisk flour, sugar, baking powder, and salt in a bowl. Set aside.
Mix softened butter, cream cheese, egg, and vanilla until fluffy, 2–3 minutes.
Stir dry mix into wet just until combined. Don’t overmix.
Gently fold in blueberries to keep the batter light.
Mix brown sugar, flour, and cinnamon until crumbly.
Pour batter into pan, smooth top, and sprinkle crumbs. Bake 30–35 minutes, until a toothpick comes out clean.
Cool in pan for 15 minutes, then slice and enjoy.