Easy project, use lightweight cotton.

Cut a circle around the intended bowl two inches away from the rim. I use pinking shears to avoid fraying

Press over a hem of about an inch (lots of tucks and folds).

Sew around the hem. This creates a channel for the elastic. Leave a gap of a couple of inches.

Cut elastic an inch longer than a snug fit length around the bowl. Stick a safety pin through the elastic and thread it around the channel. Fix the safety pin through the other end of the elastic to check the fit. If ok, Zig zag over the overlapped elastic and finally stitch up the gap in the channel.