Preheat the oven to 350°F.
Grease a 24-count mini muffin pan thoroughly.
In a large mixing bowl, combine the chocolate cake mix, all-purpose flour, cocoa powder, cold coffee, vegetable oil, eggs, sour cream, granulated sugar, salt, and vanilla extract.
Mix with a hand mixer or whisk until the batter is smooth and fully combined.
Scrape down the sides and bottom of the bowl to ensure there are no dry pockets of ingredients.
Spoon or scoop the batter evenly into the prepared mini muffin cups.
Do not overfill the muffin cups.
Bake for 10 to 12 minutes, or until the cake bites are set.
Check for doneness by inserting a toothpick into the center of a cake bite. The toothpick should come out clean or with a few moist crumbs.
Remove the pan from the oven.
Allow the cake bites to cool in the pan for several minutes.
Carefully remove the cake bites from the pan.
Transfer the cake bites to a platter or wire rack.
Repeat the baking process with the remaining batter if using one mini muffin pan.
Allow the cake bites to cool before frosting.