Preheat the oven to 350 degrees F.
Pit the peaches, remove the peach skin, and slice. Medium slices work best. Set aside.
Rinse off the blueberries and drain. Set aside.
Add 6 tbsp of butter to the baking dish. Melt butter in the 350 degree oven. Be sure to watch it carefully so that it does not burn.
Sift the flour into a large bowl.
Add the sugar, baking powder, cinnamon, and cardamom to the sifted flour. Whisk to combine.
Pour the milk into the dry ingredients. Stir until just combined. The batter will be on the thin side.
Slowly pour the batter over the melted butter. Smooth out the batter with a spatula, but DO NOT STIR. The cake will cook on top of the butter.
Gently place peaches on top of the batter.
Add the blueberries evenly among the peaches.
Lightly sprinkle the top of the cake with sparkling sugar for a crunchy topping.
Bake for 45-50 minutes until golden brown. A sharp knife or wooden skewer inserted into the cake will come out clean.