Prepare a 9x9 inch square baking tin with non-stick baking paper.

Place your marshmallows and butter into a large saucepan and allow to melt on a low heat. Keep stirring so it doesn't stick to the bottom of your pan.

Once smooth and very sticky remove from the heat and add your rice krispies to the pan. Mix them so all the krispies are coated. If your saucepan is too small to cope with this, transfer into a large bowl and mix.

Then place your mixture into your tin. Press it down as tightly as you can, it's very sticky but I find it becomes less and less sticky so keep pushing it in.

Melt your milk chocolate in the microwave or in a bowl over a saucepan of boiling water on the hob. If you melt it in the microwave, make sure you mix it every 20 seconds or so to ensure the chocolate doesn't burn.

Once the chocolate is melted pour it over your krispie square and make sure it is evenly spread across the top.

Cover the melted chocolate with as many M&M's as you like!

Place in the fridge to allow to completely set.

Once set, remove from the tin and cut into squares - either 9 big squares or 16 small ones.