Start with 6 sc in a magic loop and keep doing sc in sc with evenly spaced increases to make a flat disc.
Sl st in every sc when you reach the desired size. Then do sc not into the sl sl you just made, but into every sc of the previous round - this gives you a very neat transition from bottom to wall (see picture)!
Keep doing sc in every sc from that point without increasing. To make a scalloped edge I did a simple sc-dc-trc-dc-sc repeat on the last round.

Machine washed on 60 degrees Celcius - but it turned out I didn’t need it that hot. It shrunk like crazy!