Preheat the oven to 180°C. Grease a 20 cm round cake pan and line it with parchment paper.
In a large bowl, mix 200 grams of all-purpose flour, 1 teaspoon of baking powder, and a pinch of salt. Set aside.
In another bowl, cream together 100 grams of softened unsalted butter and 150 grams of granulated sugar until light and fluffy.
Add 2 large eggs, one at a time, to the butter-sugar mixture, mixing well after each addition. Stir in 1 teaspoon of vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with 120 ml of milk, beginning and ending with the dry ingredients. Mix until just combined.
Gently fold in 250 grams of fresh blueberries into the batter.
Pour the batter into the prepared cake pan and spread it evenly.
For the crumb topping, mix 50 grams of all-purpose flour, 50 grams of granulated sugar, 1/4 teaspoon of ground cinnamon, and 30 grams of cold unsalted butter (cut into small pieces) in a bowl. Use your fingers to combine the ingredients until a crumbly texture is achieved.
Sprinkle the crumb topping evenly over the cake batter.
Bake the cake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.