Cook first 3 ingredients in olive oil in a large Dutch over over medium-high heat, stirring constantly, until tender.  Cool slightly, then place about 1/4 of the mixture in a blender.  Add 1/2 cup brother and process until smooth.  Pour into a wire-mesh strainer and strain into a large bowl, discarding pulp.  Repeat with remaining peppers and another 1 1/2 cups broth.  Place processed peppers, remaining broth, salt, and curry powder into the Dutch oven.  Bring to a boil over medium heat, then reduce to low and simmer for 15 minutes.  Cool, and then whisk in buttermilk.  Cover and chill; serve cold.