- Butter and line a 20 x 10-cm (8 x 4-inch) loaf pan with parchment paper. In a saucepan, bring the sugar, corn syrup, butter and water to a boil. Simmer for about 15 minutes or until a candy thermometer reads 116 °C (240 °F). Remove from the heat, add the cereal and blend well. Spread into the pan and allow to cool. Cut and wrap the bars individually in plastic wrap.