Cream the butter and sugar together until fluffy and creamy in an electric mixer.

Add the egg and vanilla and mix for 1 minute more.

Add the flour and mix with a spatula to form a dough.

Wrap the dough for 30 minutes in the fridge.

Take teaspoons of the dough mixture and roll into balls place on a lined oven tray.

Press down on each ball and then add the M &Ms.

Bake for 15 minutes.

Cool on the tray for 5 minutes then transfer to a wire rack.