Line an 8-inch square baking pan with parchment paper and set aside. In a medium bowl, whisk together the cocoa powder, maple sugar and 1/2 teaspoon salt. Whisk in the warm melted cacao butter and vanilla until smooth. Gently stir in the cereal and peanuts; pour into the lined pan and, using an offset spatula, spread evenly. Scatter some peanuts over the top and let set overnight at room temperature or refrigerate until firm, at least 2 hours. Cut into squares and serve.