Add the Greek yogurt, peanut butter, cocoa powder, honey, vanilla, and salt to a mixing bowl or blender.
If using protein powder, add it now along with the milk.
Blend or whisk until completely smooth and creamy.
Transfer the mixture to a freezer-safe container.
Freeze for about 4 hours, stirring vigorously with a fork every hour to help create a creamier texture.
Let the frozen yogurt sit at room temperature for 5–10 minutes before scooping.
Top with shaved dark chocolate, chopped peanuts, cacao nibs, or a drizzle of melted peanut butter if desired.
