Preheat oven to 375 degrees F.
Make the vegan buttermilk by combining the almond milk with apple cider vinegar. Mix and place back in the fridge until ready to use.
In a large bowl, add the peaches, blackberries, sugar, and cornstarch. Mix with a spoon until well combined. Set aside.
In another large bowl, add the flour, salt, sugar, and baking powder. Mix until combined. Add the cubed butter and using a fork, cut the butter into the flour until it resembles coarse sand and is evenly distributed throughout the flour. Pour in the cold vegan buttermilk from the fridge. Stir with a spatula until everything is combined. Careful not to overmix. It will be a wet, sticky dough.
Grease a 10 inch cast iron skillet, or baking pan of similar size (9×9 square pan would work), and pour fruit filling into the skillet.
Using an ice cream scoop or large cookie scoop, scoop topping into 8 portions over the fruit filling. It is fine if there is a little space between the cobbler topping. Lightly brush the cobbler topping with almond milk. Sprinkle 1 Tbsp of sugar all over the cobbler topping. (Brushing the tops with milk and adding sugar over it creates the extra crispy tops that we are looking for so don’t skip this step!)
Bake for 50-60 minutes or until top is golden brown. Let it sit for 20 minutes before serving. Eat warm with ice cream and enjoy! Best when eaten fresh/day of. If you plan on serving it that same day, don’t cover the cobbler because it will make the topping soft. Store leftovers in an airtight container on the counter or fridge. The topping won’t be crisp the next day but the cobbler will still be delicious. You can warm leftovers up in the microwave too.