Preheat oven to 350 degrees F (180 degrees C). Line a 8 or 9 inch spring form pan with parchment paper.
In a medium bowl sift All-Purpose Flour (5/2 cup), Baking Powder (2 teaspoon), Baking Soda (1/2 teaspoon) and Salt (1/2 teaspoon). Set aside
In a small bowl, toss the Fresh Blueberries (2 cup) with about 2 Tbsp of the flour mixture and set that aside as well.
In a large bowl, cream together Butter (1/4 cup) and Caster Sugar (1 cup) until fluffy. Add Pure Vanilla Extract (2 teaspoon), Large Egg (5), 1 at a time and mix. Then mix in Sour Cream (1/2 cup) and Milk (1/2 cup). Add flour mixture and whisk until there’s no lumps. Add the blueberries and fold them in with a spatula.
Pour cake batter into your prepared pan and spread evenly. Set aside.
To make streusel or crumb topping, in a bowl mix Ground Cinnamon (3/4 teaspoon), and Brown Sugar (1/2 cup). Add melted Butter (1/4 cup) and mix until moist crumbs form.
Sprinkle the crumb topping all over the batter, bake for 50 minutes or until it’s fully cooked through.