1. Mussels cook very quickly and will turn rubbery when overcooked. To prevent that, pick out the mussels as they open and transfer to a bowl until all the mussels are cooked.
2. To crush the sesame seeds, use a mortar and pestle or place it in a Ziploc bag and crush it with a rolling pin or bottle.
3. You can substitute shelled mussels with frozen mussels. If you use frozen mussels, you can skip the first 3 steps.