Working on this second baby sweater. I had to take the needle out of it yesterday due to a unintentional short row. So, I laid her out for a photograph. This is the Zimmerman "baby surprise" idea, with a modification that has probably been done before.
The basic "surprise" you make the back section from the shoulder to the armpits. Then you make sleeves. Then you knit the second half of one sleeve, the back, then half of the second sleeve together. Then knit back and forth, increasing two stiches at the join in order to make the miter.
My modification is shown here.
I accomplish it by knitting the two sleeves, and make sure that I have an even number or stitches.
I slip the stiches for the back half of one sleeve onto the needle and knit to where the back should begin. Then I use a temporary cast on to add the back stiches, then I knit across half the second sleeve. I then knit back and forth, decreasing two stiches at the back/arm join. It makes this sweet mitered back section, and saves me a bit of seaming.
I'm sure this has been done before.