Cast on a number of stictches multiple of 4 and knit 6 rows 2/2 ribbing in the round.
Knit in the round until desired length.
Distribute the stitches on DPNs so that you have an even number of stitches in each needle and knit 2 stitches together to the end of row. You now have half the stitches that you casted on.
Knit 1 row.
If necessary, distribute the stitches by the needles so that you have an even number of stitches in each needle.
Knit 2 stitches together to the end of row. You now have a quarter of the number of stitches you casted on.
Knit 1 row and cut the yarn, leaving about 6".
With a tapestry needle, pass the yarn trough each stitch, take them off the needles and pull the yarn to close the top of the hat.
Weave in ends.