Outer pot (cotton drill): Sew the short ends of your rectangle together with the right sides together to form a cylinder shape. Press the seams open. Do the same for your inner pot (lining)
By folding in half and half again, find the quarters of the circular base and mark. Do the same to the cylinder using the seam as the CB. Pin the base to the cylinder with right sides together matching up the quarter marks. Stitch.
Clip into the seam allowance all the way around the base to release any tension (this will help it to sit better).
Tuck one pot inside the other one making sure the right sides are together and pin. Sew them together ensuring that you leave a 10cm gap for turning through.
Turn everything through to the right side and press the seam allowance and tuck it into the gap. Slip stitch the gap closed with a needle and thread.
Or if you prefer you can edge stitch is closed using the sewing machine.
Tuck the lining inside and arrange the turned edge.