Place the cereal in a bowl. In a saucepan combine the brown sugar and corn syrup and bring to a boil. Boil for 1 minute then turn off the heat. Stir in the peanut butter then pour it over the cereal and stir immediately to combine and coat. Press into greased mini muffin tins (you'll probably need 3 tins) and let cool to set about 15 minutes. Pop out and store at room temperature.