Nice mallet!
I use a parting tool to bring the tail end down to about 1/4 inch or a little less, then part the top off. Loosely hold the large end of the mallet in your hand as you make the final cut so it doesn't go flying.
Then cut off the little excess off the small end and sand smooth.
Thanks Mike. I was close. I got down to about 1/2" but was reluctant to go any farther so I just sawed it off. Next time I will try to finish it off like you said.