Many Southeast Asian dishes just wouldn't be the same without the fruity and citrusy sweet-sour flavor of tamarind, although I've used lime juice as a substitute during desperate times. The tamarind commonly used in cooking comes from the seed pods of the tamarind tree that can usually be found in pod form, as a hard block of pulp, as a concentrate, or in a powder form.
Tamarind concentrate and powder may present themselves as attractively convenient but I find the best results to come from making tamarind paste from the tightly packed pulpy block (preferably seedless), which is usually available at Asian stores and storable in the refrigerator for quite a long time. Based on my experience cooking in Malaysia, online research and trials at home, this is how you can prepare tamarind paste.
1. To make about 1/4 cup of tamarind paste, cut off 80-100g (about 1/2 cup) of tamarind pulp from the block. You don't have to be exact but these measurements are a useful guide.
2. Place in a bowl and add about 1/2 cup of boiling water or enough to cover the pulp. Let the pulp sit in the water for 15 to 20 minutes to soften.
3. Using a fork or your fingers, incorporate the pulp into the water as much as you can. Then pour the pulp into a fine mesh strainer atop a bowl and push the pulp through with a fork, spoon or spatula to separate the pulp from the fibers (and seeds).
4. The result of all that hard work is a tamarind paste the consistency of apple sauce. It's not difficult although the process can get a little messy and requires some patience. I usually make a big batch of tamarind paste and portion it out into freezer bags to be frozen for later use.
Use it! Tamarind paste is used to make Malaysian Laksa with Pumpkin (Spicy Noodle Soup).