Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan, or line it with parchment paper for easy removal.

In a small bowl, mix the flour, brown sugar, cinnamon, and salt for the crumble topping. Add the cold butter cubes and use your fingers or a pastry cutter to work the butter into the dry ingredients until it forms coarse crumbs. Set aside.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt for the cake batter.

In a large bowl, cream the softened butter and granulated sugar together until light and fluffy (about 3-4 minutes).

Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the sour cream or Greek yogurt, beginning and ending with the dry ingredients. Mix until just combined—do not overmix.

Gently fold in the blueberries.

Pour the cake batter into the prepared pan and spread it evenly.

Sprinkle the crumble topping evenly over the cake batter.

Bake in the preheated oven for 40-50 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. If the topping starts to brown too quickly, cover the cake loosely with aluminum foil in the last 10-15 minutes of baking.

Allow the cake to cool in the pan for 10-15 minutes, then transfer it to a wire rack to cool completely. Serve the cake warm or at room temperature.