I made a kind of fan-shaped design for mine.
Start by cutting a square of muslin slightly larger than you need. (The square will shrink slightly when you sew onto it.)
Draw pencil lines from those notches to the 90 degree corner opposite.
Place your fabric covering the middle section on the other side (not on the pencil-lined side), good side facing outward.
Place a second fabric, good sides facing the first fabric. Your fabric is not visible as it is on the underside of the muslin square.)
Sew along the pencil line. (This is how you would sew when paper piecing.)
Iron between strip additions.
Continue to cover the muslin with fabric strips and trim the block to the size you need after the muslin is completely covered.
Attach it to the border and sew it onto your quilt.