If you see an elfand you have an empty cauldron, than quickly brew up a potion that usually takes a long time to brew. Then talk to him. He'll help you brew it a lot quicker.
Make Potions Faster
To do this go to 'Settings' on your device and change the time/date to the future. When you do this your potions will be made at lightning speed and give you the amount you would have made in that time period. It will also allow you to spin for prizes. When your potion is done just reset your time/date back to the present.