To make Cupcake fridge magnets, you need,
Some nice paper
Craft foam (2 colours)
A button
Some sparkly thread
Craft Magnets

Step 1:

Make yourself a couple of templates if you're going to make several, one for the cupcake top and one for the bottom.
Draw around the bottom template on some nice flowery paper. If you use a thick coloured pen, when you cut it out and it makes a nice outline.
Draw around the top template on some white or light coloured craft foam.

Step 2:

Cut out the foam and paper top and bottom and stick them onto the darker colour foam.
Thread the sparkly thread through the button and stick it in place with double sided tape. Tidy it up and stick it to the top of the cupcake.
Cut the foam around the cupcake leaving a bit of an outline.

Step 3:

Stick Magnets on the back

Step 4:

All finished.

You used to be able to get magnet-backed foam that you could use instead; but I've not been able to find any for a while - it's probably still out there somewhere though...