In a large skillet, melt 1/2 the butter over low heat. Add the onion and mushrooms and cook until most of the liquid has evaporated, 5 to 6 minutes. Combine the mushroom mixture, Port, soy sauce, Worcestershire sauce, cumin, and coriander in the bowl of a food processor and process until smooth. Cut remaining butter into pieces and add to mushroom mixture. Process again until well blended. Press mushroom spread into a lightly oiled mold or small bowl, wrap in plastic, Cover and refrigerate several hours or overnight. To serve, unmold onto a serving plate. Makes 6 to 8 servings.