I did it!
I ruined the first pair of mittens!
And it took all afternoon on Sunday to do it. Fortunately, I'm pretty sure I still have enough fabric left on the back and other sleeve of this sweater to make a second, more presentable pair.
These ones will do fine for snow shoveling and, perhaps, snowman making, but they're not good enough to gift, for reasons that have nothing to do with my apparent lack of sewing finesse:
1/ the pattern calls for a single layer, which means you're touching the interior seams with your fingertips all the time and will freeze.
2/ an interior layer, with the right side touching your hands, solves both these problems.
3/ even if you cut both sets of mittens from two entirely different weights of fabric, they won't nest nicely if you cut them the same size.
4/ I'm not entirely sure that stitching ribbing onto a giant puffy two-layer mitten is the best way to get a finished look.
5/ plus, you get another annoying seam inside, rubbing against your wrist.
I think I'll ruin a second pair after adapting the pattern for a longer hand to replace the ribbing, and a slightly larger set of pieces for the outer layer. But I'm going to try not to wait until next Sunday afternoon to find time for this, because I am supposed to make 12 pairs in the next 5 weeks - plus shortbread.