In a small heavy skillet cook onion, bell pepper, and garlic in butter over moderately low heat, stirring occasionally, until softened. In a bowl mash one-third beans with a fork and stir in remaining beans, onion mixture, bread crumbs, egg, coriander, salt, and pepper to taste.
Form mixture into four 4-inch patties. (Mixture will be wet and soft.) Gently dredge patties in cornmeal and transfer to a large plate lined with plastic wrap.
In a heavy skillet heat 1/4-inch oil over moderate heat until hot but not smoking and cook patties in 2 batches 1 1/2 minutes on each side, transferring to paper towels to drain.
Serve bean cakes with salsa (recipe follows
Recipe Courtesy of Gourmet Magazine