Hutch

My struggle is with stitching a french seam using a machine with three of the bag sides already stitched.

I'm starting on my first project, a leather tote for my wife made from upholstery weight leather. I need advise on how to finish a seam. The pattern consists of 2 square panels machine sewn on 3 sides. Getting all 3 sides sewn together is easy enough, however, I'm at a loss as to how to achieve this type of seem. I cant figure out how to complete the 2 stitches on either side of the first seem with a machine.