Preheat oven to 180°C (350°F) and line a 9" baking pan with baking paper and set aside.
Cream together the butter, sugar and brown sugar.
Beat in the eggs, vanilla, and ¾ of the peanut butter and mix well.
Add in the oats, flour and baking soda and mix.
Press into the baking pan and place in the oven to bake for 15-20 minutes. They will look slightly underdone in the middle and will harden as they cool.
While still warm, spread over the remaining ¼ cup of peanut butter.
Allow to cool while you make the chocolate topping.
Melt the peanut butter and chocolate together until smooth and pour over the cooled bars.