Cut peaches into 1/4" (if they are very firm) to 1/2" (if they are very ripe) slices, toss gently with sugar, and berries.
Mix dry ingredients in bowl of stand mixer. Add butter and mix until large pea-sized pieces form. Add milk and mix just to distribute. Mixture will be dry and crumbly.
Pour fruit into the middle of a well-greased pie pan. Sprinkle crumbs over the top and around the sides. Using your fingers, pat some of the crumb mixture around the edges down towards the bottom of the pan forming a side crust. (By not having a bottom crust the fruit stays fresh and the cobbler stays crisp.)
Bake for 35 to 40 minutes until crumble is golden brown on top and edges.