In a large bowl, beat together the butter, golden syrup and sugar until fluffy.
Beat in the egg and the vanilla until well combined.
Add the flour and the baking powder and mix well – you should now have a sticky, light dough.
Fold in the white chocolate chips and all but a handful of the M&Ms.
Use a large ice cream scoop the dough, flattening off against the side of the bowl, then roll the dough into a ball with your hands. This is the best way to get 16 equally sized cookies.
Place the balls of dough on baking sheets lined with greaseproof paper, being sure to place each cookie at least an inch apart so that they don’t stick together when they spread.
Pop a 3-4 extra M&Ms on top of each cookie.
Bake for 8-10 minutes until golden at the edges. Get them out of the oven before they’re fully browned so that they stay chewy when cool.
While still hot, place a tumbler over a cookie and gently move it in small circles to bring the cookie into a neat circle. Repeat with all of the cookies - this only works when they are fresh from the oven and soft.
Allow to cool on the tray until firm enough to transfer to a wire rack to cool completely.