Preheat the oven to 350 degrees F and place a rack in the center of the oven. Grease the sides of a 9-by-3-inch round cake or bundt pan.
Sprinkle the brown sugar in the pan and pour in the melted butter. Top with the peaches and blueberries and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the sugar with the room temperature butter on medium speed until fluffy, then increase to high speed for 3 to 5 minutes. Turn off the mixer, add the cream cheese ,and then mix on medium speed.
In a medium bowl, whisk to combine the flour, baking powder and salt.
Turn the mixer off and add the eggs, then mix on low speed to beat in the eggs. Add the flour mixture slowly, then add the milk and vanilla extract and mix until combined. Spread the batter over the fruit and transfer to the oven.
Bake until a toothpick inserted in the center comes out clean, 1 hour.
Transfer the pan to a wire rack to cool for 5 minutes, then run a knife around the sides to loosen the cake and invert onto a plate. Let cool and serve.