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

In a mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.

In another bowl, cream the softened butter until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, until just combined. Fold in the blueberries.

In a small bowl, mix together the flour, sugar, and cinnamon. Stir in the melted butter until crumbly.

Pour the batter into the prepared cake pan and sprinkle the topping evenly over the batter.

Bake for 30-35 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.