Heat
the oil in a saucepan over medium heat. Add the cumin seeds, ginger,
cayenne pepper, fennel seeds, asafoetida powder, and garam masala; cook
and stir for about 2 minutes to release the flavors.
Stir
the water into the pan with the spices along with the sugar and
tamarind paste. Bring to a boil, then simmer over low heat until the
mixture turns a deep chocolaty brown and is thick enough to coat the
back of a metal spoon. This should take 20 to 30 minutes. The sauce will
be thin, but it will thicken upon cooling.