Follow these simple steps to create your own delectable blueberry upside-down cake:

Preheat and Prepare: Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.

Melt Butter and Sugar: Melt the butter and pour it into the prepared cake pan. Sprinkle the brown sugar evenly over the melted butter.

Arrange Blueberries: Arrange the fresh blueberries in a single layer over the brown sugar.

Mix Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

Prepare Batter: In another bowl, beat the granulated sugar and eggs until light and fluffy. Mix in the vanilla extract. Gradually add the flour mixture to the egg mixture, alternating with additions of sour cream and milk, beginning and ending with the flour mixture. Mix until just combined.

Pour Batter: Pour the batter over the blueberries in the cake pan, spreading it evenly.

Bake: Bake the cake for 40-45 minutes, or until a toothpick inserted into the center comes out clean.

Cool and Serve: Let the cake cool in the pan for 10 minutes, then invert it onto a serving plate. Serve warm or at room temperature.