Grease and line an 8x8-inch baking tin.
Place cereal in a large bowl and set aside. In a small saucepan, combine peanut butter, salt, rice malt syrup and vanilla. Heat gently and stir until thoroughly combined and melted.
Pour the peanut butter mixture over the cereal and stir until all the cereal is coated.
Transfer the peanut butter cereal to the prepared tin and spread out evenly. Place a piece of parchment paper on top of the cereal and use another pan, or your hands, to flatten the top.
Place the tin in the refrigerator to set for around 30 minutes.
Near the end of the 30 minutes, place the chopped chocolate and 1tablespoon peanut butter in a heatproof bowl set over a pan of gently simmering water (water should be about 1-inch high and the bowl should not touch the water), ensuring no water comes in contact with the chocolate mixture. Stir occasionally until melted and smooth.
Take the peanut butter cereal from the refrigerator, pour the melted chocolate on top and smooth the surface. Return to the refrigerator for another 30 minutes or until chocolate is set.
Cut into squares with a sharp knife, cleaning the knife after each cut.
Store in an air-tight container in the refrigerator; let them warm up to room temperature to soften up the chocolate before serving, if desired.