I’m not going to claim to have invented this at all.. There is a very good article that explains how to get different shapes for the circle of confusion when doing extreme DOF effects like the above.Using a Canon 50mm f/1.8 lens, some card, scissors and some Blue Peter style creativity, as at DIYPhotography.net, you can create shapes in the out of focus portions of your picture.
The hardest to cut out was the snowflake, it took a bit of dexterity since the shape should only be as large as the aperture when the lens is wide open, about 1.5cm across! Good old craft knife came in handy (get an adult to help you when using sharp implements!!)
Here are some more examples…