Preheat the oven to 180°C and line a 12 hole cupcake tin with cases.
In a large bowl beat butter and sugar until creamy and then add the peanut butter and beat again.
Add the milk and eggs and beat again. Fold in the self raising flour, bicarbonate of soda and salt.
Divide the mixture between the 12 cupcake cases and bake in the oven for around 20-25 minutes, until a skewer comes out clean. Remove from the oven and leave to cool.