Here's how I made it:
Approximately 110 yards worsted weight yarn (I used 60 grams of Malabrigo Merino Worsted in the colorway Polar Morn)
Size 9 (5.5 mm) 16" circular knitting needles
Size 13 (9 mm) 16" circular knitting needles
Size 13 (9mm) double pointed needles
Cast on 89 stitches using size 9 needles. I cast on 89 because I like to use
method for joining in the round, so that there is no small gap. If you don't want to use this method, just cast on 88 stitches.
Join in the round being careful not to twist stitches. You can place a marker if you like; I just use the tail as a guide for the beginning of a row.
K1, P1 for 5 rows.
Switch to size 13 needles and continue K1, P1 in the round for 5.5 inches.
Switch to DPNs.
Next round ssk all the way around.
Knit two rounds.
Next round k2tog all the way around.
Cut yarn, thread darning needle and draw the needle through the remaining stitches on the needles. Pull tight to close and pass yarn through middle to the inside of the hat.
Make a large pom pom. I made mine by wrapping the yarn around the palm of my hand 100 times, securing the center with a tight knot to make like a bowtie and then cutting all of the loops and trimming until it looked the way I liked. There's a good tutorial
on making pom poms that can help you if my description of what I did wasn't good enough. :)
Attach your pom pom to the top of the hat and weave in all ends.