I would use a circle cutter. Cut it out of fondant mixed with a little tylose. Or use 50/50 fondant/gumpaste. If you want to make them bigger than your cutter, find something with a lid the size you want and trace around it with an exacto or wheel cutter. Then use the same cutter to cut a small moon shape at the bottom of the ears to form on the hat. Depending on the size, you may need to stick a couple toothpics or skewers into the bottom to stick onto the hat. Let them dry for a day or so to firm up. Use some gum glue to glue the ears to the hat.
This is how I did ears for my mickey mouse. It was an actual mickey mouse head but I would think you'd do the same thing for a hat.
http://cakecentral.com/gallery/1947204
http://img703.imageshack.us/i/ccmickeyears.jpg/ This is only a piece of the whole hat for my own project this weekend, but here's an idea for you. The hat is formed over a half ball of styrofoam, and the ears are 2 pieces of round GP with skewers in between for inserting into the hat part. I extruded pieces of gp rope and applied the name in Disney font.
I did mine the same way - cutting out circles and then cutting away a small area so it would fit on the hat part. Here is my picture with a description of how I made the ears/hat. I used melted chocolate for glue. http://cakecentral.com/gallery/1413363
Make sure you post pics so we can see yours. Good luck and have fun!
I'm glad you asked because I have a mickeymouse cake I need to make for a coworker's college graduation party. Thanks for the ideas ladies!
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