01 - Preheat oven to 350°F. Grease a 9-inch round cake pan and line the bottom with parchment paper.
02 - Pour melted butter into the bottom of the prepared pan. Sprinkle evenly with sugar. Distribute blueberries over the sugar and drizzle with lemon juice.
03 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
04 - Beat butter and sugar together until light and fluffy. Add eggs one at a time, beating well after each addition. Mix in vanilla extract.
05 - Mix in half of the dry ingredients, then add sour cream and milk. Stir in the remaining dry ingredients until just combined.
06 - Carefully spoon the batter over the blueberry layer and smooth the top.
07 - Bake for 35 to 40 minutes, or until golden and a toothpick inserted into the center comes out clean.
08 - Let cool in the pan for 10 minutes, then run a knife around the edge. Place a serving plate over the pan and invert to release the cake. Remove parchment paper and cool for at least 20 minutes before serving.