Rinse the shells well. Heat the olive oil in a large stockpot over medium heat. Add the shells and sauté, stirring often, about 10 minutes. Add the remaining ingredients, adding more water if needed to cover the shells. Bring to a boil, reduce the heat, and simmer uncovered for 1 hour, skimming the scum from the surface often. Strain through a cheesecloth-lined strainer into a large saucepan and reduce by half. If not using immediately, let cool to room temperature, then refrigerate or freeze.
© 1992 Joyce Goldstein. All rights reserved.