Preheat oven to 350°F. Line the baking pan with parchment paper lightly.
Prepare the Crumb Topping
Mix flour, brown sugar, and cinnamon. Add cold butter. Rub until crumbly. Set aside.
Cream Butter and Sugar
Beat butter and sugar together until light, fluffy, and pale.
Add Eggs
Add eggs one at a time. Mix well after each addition.
Add Vanilla and Sour Cream
Add vanilla extract and sour cream. Mix gently until smooth.
Mix Dry Ingredients
In another bowl, mix flour, baking powder, baking soda, and salt evenly.
Combine Batter
Add dry ingredients to wet mixture slowly. Mix just until combined.
Fold Blueberries
Gently fold blueberries into batter using a spatula.
Spread Batter
Spread batter evenly into prepared baking pan. Smooth the top lightly.
Add Crumb Topping
Sprinkle crumb topping evenly over the batter.
Bake the Cake
Bake for forty-five minutes until golden and a toothpick comes out clean.
Cool Before Serving
Let cake cool for fifteen minutes before slicing and serving.
Notes
Use fresh blueberries for best flavor. Do not overmix the batter. Keep butter cold for crumb topping. Check cake center with toothpick. Cool slightly before cutting slices.