Combine muesli, Rice Krispies, coconut, sunflower seeds, sesame seeds and cranberries in a large bowl and set aside.
Combine butter, honey, peanut butter and sugar in a small saucepan and stir over a medium heat until the sugar dissolves.
Bring to the boil, reduce heat and simmer, stirring continuously for 5-10 minutes until slightly thickened. Remove from heat and add to dry ingredients. Mix well.
Press into an 18x28cm greased, rectangular baking pan and refrigerate until set.