This dip is made from mature, or brown, sour tamarind. This should be peeled before use, and the fibrous strands within the pod, and the seeds of the fruit discarded. You may also buy tamarind in a compressed block, and this is equally suitable. This recipe is an example of Thai unwillingness to let anything go to waste: tamarind water is used as an ingredient of many dishes, and is prepared as shown below. Yet this dip is something to use the tamarind paste that otherwise might be discarded. In general we make tamarind juice (nam makham piag), when we need to use it. All that is required is to store the paste in a jar until you have enough to make the dip. However don't make the mistake we did once of using a Tupperware container to store the paste - the tamarind stained it and we were never able to get it clean. Use a glass preserving jar and keep it in the refrigerator. Place two tablespoons of tamarind paste (3 if the seeds are still in place) in a jug, and pour 1 cup of boiling water over it. Leave to steep for 15 minutes, then mash thoroughly and leave to steep for a further 15 minutes. Pour the mixture through a muslin bag, and squeeze thoroughly to extract as much juice as possible. The juice is nam makham piag (tamarind juice), and may be used in other recipes. Ensure that you discard any remaining seeds or fibrous material from the pulp and reserve it. You need 1 cup of "exhausted" tamarind pulp for this recipe. Pound the shrimp in a mortar and pestle. Dry fry the chilis until aromatic, then crush. Place the shallots and garlic, unskinned, under the grill or broiler, and toast until aromatic and the skins begin to discolor, then peel and chop. After preparation you should have the quantities listed. Fry the shrimp paste in a very small amount of oil until aromatic. Combine the ingredients and grind to a smooth paste in a mortar and pestle (or food processor), then fold in the tamarind paste. Serving & Storage Accompanies fish dishes or vegetable crudits. Will keep 2-3 weeks in a refrigerator.