Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and line a few baking trays (or however many you own) with baking paper
Mix the butter, peanut butter and golden caster sugar together ideally with an electric mixer
Add the egg and mix in
Mix in the plain flour and baking powder
Mix in the chopped up peanut butter cups
Take blobs of the mixture and roll them into balls with your hands, place onto the lined baking trays, leave space between the cookies as they will spread
Optional: chill the cookies for 30-60 minutes before baking for thicker cookies that don't spread as much
Bake the cookies for 12-14 minutes until they are golden brown, leave them on the tray for 10 minutes before carefully removing and placing on racks to cool fully
To decorate, dip half of the cookies into the milk chocolate and sprinkle on the crushed Reese's Pieces. Place onto a sheet of baking paper to set
Store in an airtight container and eat within 3 days. They also be frozen without the decoration
Notes
You could use chopped up peanuts instead of Reese's Pieces if you like.
Although I provide cup measurements, I highly recommend weighing your ingredients out using digital kitchen scales*. It is the most accurate way to measure ingredients and will ensure the best results. Digital scales are very low cost and can be purchased for around £12 ($16.50) .
For teaspoon (tsp) and tablespoon (tbsp) measurements, please use measuring spoons* and not the type of spoons you eat with. Again this will ensure accuracy and provide the best results.