Grease the inside of the slow cooker with nonstick baking spray.
Add the 1 cup all-purpose flour, 2 tablespoons granulated sugar, 1 teaspoon baking powder, and 1/4 teaspoon ground cinnamon to a medium bowl. Whisk until combined.
In a separate small bowl, whisk together the 1 large egg, 1/4 cup milk, and 2 tablespoons vegetable or canola oil.
Add the wet ingredients into the bowl of dry ingredients and stir until combined.
Spread the cobbler in the bottom of the prepared slow cooker.
Berry Filling
Add the ¼ cup all-purpose flour, 1 cup granulated sugar, and 1/8 teaspoon salt to a large bowl. Stir it combine.
Add in the 4 cups frozen mixed berries and continue to stir until the berries are coated with the dry ingredients.
Spoon the berry mixture over the batter in the slow cooker.
Place the lid on the slow cooker and cook on high for 2 hours. If you want to suck up some of of the moisture, place a paper towel between the slow cooker and it's lid.
Serve warm topped with ice cream or whipped topping.
Notes
Storage: Store in an airtight container in the refrigerator for up to 4 to 5 days.