Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition.

Stir in the milk and mix until combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Fold in the blueberries gently.

Pour the batter into the prepared cake pan.

In a bowl, combine flour, sugar, and cinnamon.

Add the cold cubed butter and mix with a fork or pastry cutter until crumbly.

Sprinkle the streusel topping evenly over the cake batter.

Bake in the preheated oven for 40-45 minutes or until a toothpick inserted into the center comes out clean.

Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.