Amazingly enough, in the 40+ years I've been knitting, I've never made a Tam O Shanter. But I found this really cool pattern for Three Tams at Knitting Pattern Central. The patterns were designed by the very talented Angela Wu (see her blog here).
So I know you're looking at this picture and wondering, "how in the heck is she going to get that goofy looking thing turned into a tam?" And here's where the real magic comes in. After washing and squishing all the excess moisture out of the hat, you just stretch it over a dinner plate.
It's easy to center the plate correctly and evenly with this pattern. Isn't the top shaping beautiful?
Here's what the bottom side looks like. I love how this turned out and the really neat thing is that the contrasting colored yarn (Noro Kureyon) changes colors all by itself within the skein. Once the hat has dried, I just take out the dinner plate and it's ready to wear or more likely be given away as a gift.