It took almost all of Saturday for me to figure out the most back-friendly place to cut is my very own laundry room, complete with a ceiling light positioned perfectly over the washer:

I ditched the separate cuff and extended the wrist, which worked better with the liner mitten I'm putting inside each pair.


I was so pleased with myself, I sewed together both of these pairs before the thought occurred to me to try them on a guy, who pointed out that the seam across the middle of the palm was pulling in a decidedly uncomfortable way. But that's all right, because I only need one pair for a guy - everybody else on my mitten list is a girl.
I cut a wider pair from a really exciting find - an XL man's elaborate, colourful, and all-wool Fair Isle cardigan from one of my favourite posh-ish shops - and sewed them together:

But they pulled, too.
Still, not a complete disaster! I can still gift these to a girl.
(Me, for example.)
I slept on it, then decided to come up with an entirely new pattern with just a front and a back piece. I gambled on the manliest stripe in my felted sweater stash and got this:

They fit Tester Guy perfectly. Cut down a little, they'd fit me perfectly too. In fact, I'm so in love with them, I want to make all the rest of the Christmas mittens with this pattern - but I can't, because you can really only get one pair out of a whole sweater and I've ruined quite a few already with my early, sadly non-giftable, efforts.
Options:
Cutting and stitching 60 pieces of mitten from the remaining stash or
Shopping for ten more feltable sweaters
H'mmmmmmmm......