I'm working on the "Baby Bolero" pattern from Debbie Bliss Baby Cashmerino 2. The finishing involves sewing a separately knitted garter stitch border to a stockinette stitch garment. What stitch should I use so that the border lies flat? Thanks!!
I would use mattress stitch.
I've found that backstitch makes a stronger (but less invisible) seam than mattress, but if you do it carefully, it makes a great, neat seam.