Before Easter I always plant some garlic cloves so that I have fresh green garlic. It is pretty easy to do. Split garlic into cloves. In a pot put some soil ( I always use cactus soil, but I do not think that matters). Water it and put it on a sunny place, like in front of the window. After 3 days they should start growing. Of course you can do the same with onion.
Allium sativum L., commonly known as garlic, is a species in the onion family Alliaceae. Its close relatives include the onion, the shallot, and the leek. Garlic has been used throughout recorded history for both culinary and medicinal purposes. It has a characteristic pungent, spicy flavor that mellows and sweetens considerably with cooking. A bulb of garlic, the most commonly used part of the plant, is divided into numerous fleshy sections called cloves. The cloves are used as seed, for consumption (raw or cooked), and for medicinal purposes. The leaves, stems (scape) and flowers (bulbils) on the head (spathe) are also edible and most often consumed while immature and still tender. The papery, protective layers of 'skin' over various parts of the plant and the roots attached to the bulb are the only parts not considered palatable. (click for more)
Update: After 8 days they are already that high.