Preheat the oven to 170 degrees / 160 fan /Gas mark 3 and line 3 baking sheets with greaseproof baking parchment.
Cream together the butter, peanut butter and sugar.
Add the eggs and vanilla extract and mix in.
Sieve in the flour, baking powder, cocoa, bicarb and a pinch of salt.
Stir in in the flour until you get a thick mix. If is it too dry add a little splash of milk.
Add 150g of the Reese's Pieces and mix in until evenly distributed.
Take heaped tablespoons of the mix and pop them on the lined baking trays. Make sure they aren't too close together as they will spread.
Use up the last Reese's Pieces to add a few to the top of the cookies.
Bake for 10 minutes.
Allow the cookies to cool for a few seconds and enjoy. They taste lovely warm with a cup of tea.