This is a vital garnish for many spicy Chinese dishes.  While you can buy it, you should consider making your own.  It is very easy to make; you’ll have yours done with only a few minutes of work.  And, unlike what you’d buy in the store that will be months (if not years) old, yours will be fresh with a much brighter flavor.  We’ve adapted the following from James Peterson’s 1992 James Beard Foundation Cookbook of the Year: Sauces.

30-50 dry Cayenne or Asian hot peppers, destemmed
6 garlic cloves
3 tablespoons fresh ginger
3 tablespoons fermented black beans
4 cups peanut oil
½ cup dark Asian sesame oil

Chop the chiles, garlic, ginger, and black beans together by hand or in a food processor.  Your goal is 2 cups; if you are short add in more chile pepper.

Combine chile mixture with peanut oil in a heavy saucepan.  Place over medium heat.  When the solids begin to sizzle and float, reduce heat to low and cook for another 5 minutes or until they smell toasty.  Remove pan from heat and allow to cool for 30 minutes. 

Strain mixture through a fine strainer or a jelly cloth, and combine with the sesame oil.