Preheat oven to 350 degrees F. Spray a 9-inch springform pan with baking spray.
In a medium bowl, combine the flour, baking powder, salt, and cardamom.
In the bowl of a stand mixer, cream the butter until it is a pale yellow. Add the sugar and continue beating until thoroughly mixed. Add the egg and the vanilla. Add flour mixture, alternating with the milk, until well-mixed.
Pour the batter into the prepared pan and add the peaches and blackberries, spreading evenly in a pretty design. Bake for 1 hour, or until golden brown and a cake tester inserted into the center comes out clean.
Let cool completely in pan. Remove sides and dust with confectioners' sugar. Serve at room temperature
Notes
This recipe is spectacular when cooked in a cast iron skillet which causes the edges to crisp. Serve with ice cream or whipped cream, as desired.