Steal a mortar and pestle. Steal a lot of food items and turn them into potions. It should not take too long to reach the Master level.

Use the "Duplicate items" trick to duplicate two different types of food (such as apples and lettuce or other fruits). Try to get over 100 of each food. Then, use a mortar and pestle to create potions from the food. Repeatedly make potions as quick as possible with the duplicated food. When you run out of food to make the potions, just duplicate some more and repeat the process. It is possible to get your Alchemy skill to Master in ten minutes or less.