Freeze your bananas right. Peel, slice into coins, and freeze in a single layer on a parchment-lined sheet. Once solid, transfer to a freezer bag. This prevents clumps and blender tantrums.
Load the blender or food processor. Add frozen banana slices, cocoa powder, a pinch of salt, vanilla, and 1/4 cup of your chosen milk. Start with less liquid—you can always add more.
Pulse, then blend. Pulse to break up chunks. Blend on low, scraping down sides as needed. Add milk 1 tablespoon at a time until the mixture becomes creamy and thick, like soft-serve.
Adjust sweetness. Taste. If you want sweeter, add maple syrup or honey. If you want deeper chocolate, add another teaspoon of cocoa or a pinch of espresso powder.
Optional add-ins. For protein or nuttiness, blend in nut butter or protein powder at the end. For texture, stir in cacao nibs or mini chocolate chips.
Serve immediately. Spoon into a chilled bowl or glass for a Frosty-style vibe. For a firmer scoop, freeze 20–30 minutes, then scoop.