Cut the peaches in half, remove the pits and cut into slices.
Preheat the oven to 220 degrees. Combine chopped peaches with blueberries, sugar, flour, lemon juice, cinnamon and salt in a baking dish. Make cookie dough. Mix together flour, cornmeal, brown sugar, baking powder and salt. Cut the butter into pieces and add to the flour mixture. Stir with a fork or fingers until the mixture looks like crumbs.
Pour in the buttermilk and stir with a rubber spatula until the dough is moist and sticky. Spoon the cooked dough over the peaches and blueberries. Don’t worry about covering the entire surface.
Bake the cobbler until the cookies are golden brown and slightly black on the tops, 20 to 25 minutes. Let cool slightly. When serving, scoop the cobbler out of the mold. You can garnish the cobbler with whipped cream, vanilla ice cream, or any plain yogurt.