Melt butter and sugar in a deep saucepan until sugar is dissolved.
Pour oatmeal there and cook for another 3-4 minutes, stirring constantly.
In another bowl, combine the chocolate and peanut butter and melt.
Put half the finished oatmeal in the parchment-covered pan. Then put chocolate filling and the rest of the cereal. Leave a little filling to sprinkle the top.
Refrigerate for several hours. Allow the bars to stand a little at room temperature before serving and slicing.