Grind the peanuts in a blender, a few at a time, until they're mealy--about like grits. (Do not overgrind into peanut butter.)
Heat the stock in a large saucepan. Stir in onion, ground peanuts, and curry powder. Bring to the boil, then lower to a simmer and hold there for 30 minutes, stirring frequently.
Strain the soup and puree the solids in the blender, adding a little of the broth to make it smooth. Return the puree to the broth in a saucepan over low heat.
In a bowl, stir the cornstarch into the half-and-half, then stir it into the soup. Cook, stirring, until the soup is thickened. Season with salt, pepper, and Tabasco.
Cook a few minutes longer. Sprinkle with cilantro and serve very hot.
