The simplicity of a rasam is a decoy for its depth. At first sip, you may only discern the faint sweetness of a ripe tomato. Then comes the punch of tamarind. You reel momentarily from this affront, but you will soon be soothed by the nutty richness of mustard seeds fried in ghee—called the thalippu, or tempering that crowns this trellis of flavor.
For eons, South Indians of all stripes have claimed an intimate understanding of rasam, a broth (not unlike a stock) that teases complexity out of even the most minimal ingredients. At its simplest, this could mean a tomato or two, or a knob of dried tamarind and a scattering of spices—all allowed to commingle until their flavors merge into a cohesive whole.