A spur of the moment project.
Project page here.
The only modification I made was to eliminate one row of the top ribbing, since otherwise it would have been in the way for drinking from the mug. Of course, that would all depend on the size mug you use.
It only took about 2 hours to do the knitting, so it was a pretty quick project. For worsted-weight yarn and my gauge, this fit one of my smaller mugs snugly. To fit some of my larger mugs, I might add a couple of stitches. But it hasn’t been blocked, and it will probably stretch a little bit when it’s heated up.
One thing to think about if you make it: The arms may get in the way a bit when drinking, so you might want to make the sweater so that the handle is on the left as you look at the front of the sweater (like the Sugar ‘n Cream pattern). That way, the arms will be facing out as you drink.
Otherwise, the only thing I’d probably change if I make another one is to set the second sleeve back a little farther. I attached it exactly opposite the first arm, but since the first arm actually starts behind the handle of the mug, putting the second sleeve exactly opposite makes that sleeve farther to the front.
And look – the little mittens just happen to be exactly Barbie-sized: