Place the semisweet chocolate chunks, peanut butter, and softened butter in a large, heat proof mixing bowl.
Place the mixing bowl over a saucepan with about 2-inches of simmering water. Turn the heat to low and stir until the ingredients are completely melted and blended together.
Add the sea salt and vanilla to the chocolate mixture and stir well to combine.
Pour the chocolate mixture over the cereal, and stir gently with a spatula to evenly coat.