Grease a 15 cm square baking pan with oil and set aside.
Take brown sugar, 75 grams of butter in a sauce pan and bring it to a boil. Once it boils take it off the heat and add in 1 teaspoon of vanilla. mix well.
Now add oats in this and mix well. Spoon this into the pan and flatten it so it is smooth. Put this in fridge and let it chill till you make filling.
Take butter, chocolate chips and peanut butter in a sauce pan and melt on a low heat till it is melted.