I am having an idea for a bag and I believe I have seen this technique somewhere before. I just have no idea what it’s called and hence have a hard time finding a video or instructions.
Essentially I want a round corner the comes out a bit and then the gusset over the two sides. I believe I have seen an approach where you cut a side piece with rounded corners and then cut perpendicular into the middle of the corner. Then sew that cut and turn over. The corner sticks out essentially and the side is then attached to a long piece that runs from one side around as bottom and up on the other side.
I am not sure if I am explaining this well enough to ID. I will try to find a pic.
You'll have to remove a slice; if you just cut a slit, you'll have to overlap them, and you won't have enough seam allowance to connect them once you start getting to the point of the slit. If you cut a piece out, and have a backing piece of leather, you'll be able to sew all the way around.
This kind of stitching would be easiest on a post-bed roller foot machine. It's going to be a real challenge with a flat bad machine. Otherwise, I'd use contact cement to hold the backer on temporarily (or even just rubber cement), and then stitch by hand.
I only hand sew