Beat the butter and sugar together till it is light and fluffy.
Add the egg and vanilla extract and beat again until fully incorporated.
Stir in the peanut butter.
Sift in the flour, baking soda and salt and gently fold to bring it all together.
Fold in the peanut butter chips if you are using them. Then chill the dough in the fridge for at least 30 minutes.
Preheat your oven to 180C / 350F / Gas mark 4 and get a couple of large baking sheets ready.
Roll the dough out into 24 balls. When they go on the baking sheet press them flat with a fork to about 2 and 1/2 inches (6cm) wide making a criss cross pattern.
Bake in the oven for 10 to 12 minutes.
When you bring them out of the oven leave them on their tray for a few minutes before transferring them to a wire rack to fully cool down. Then enjoy.
If you keep them in an airtight tin these cookies will last 5 to 7 days.... good luck in keeping them that long!