Whisk the dry base. In a medium saucepan off the heat, whisk 2 tablespoons cocoa powder, 1 tablespoon cornstarch, and 1 scoop (about 25–30 g) protein powder until no lumps remain.
Add liquids slowly. Whisk in 1 cup milk a little at a time, making a smooth slurry so the cornstarch dissolves.
Add a pinch of salt and 1/2 teaspoon vanilla.
Sweeten to taste. Add your preferred sweetener. Start with 1–2 tablespoons zero-calorie sweetener or 1 tablespoon sugar/maple syrup. You can adjust at the end.
Cook until thick. Set the pan over medium heat and cook, whisking constantly, until the mixture thickens and gently bubbles, 3–5 minutes.
It should coat the back of a spoon.
Remove from heat and enrich. Take the pan off the heat. Whisk in 1/3 cup plain nonfat Greek yogurt until smooth and glossy. Taste and adjust sweetness if needed.
Chill to set. Divide into 4 small ramekins (about 1/2 cup each).
Press parchment or plastic wrap directly on the surface to prevent a skin. Chill 1–2 hours, or until cold and set.
Serve and garnish. Top with a few berries, a dusting of cocoa, or a sprinkle of shaved dark chocolate if you like. Enjoy cold.