Position knife blade in food processor bowl. Drop garlic through food chute with processor running. Process 3 seconds or until garlic is minced. Add beans, broth, onion, and salt; process until smooth, scraping sides of processor bowl once. Transfer bean mixture to a medium saucepan. Partially cover mixture, and cook over medium heat 15 minutes or until thickened, stirring frequently.
Combine sour cream and cilantro; stir well. Cover and chill.
Place tortillas on a baking sheet coated with cooking spray. Bake at 350° for 6 minutes; turn tortillas over, and bake 6 to 8 additional minutes or until crisp.
Place 1 tortilla on each individual serving plate. Spoon beanmixture evenly over tortillas; top each with cheese. Arrange lettuce over cheese. Top each tostada with 2 tablespoons Grilled Corn Salsa and 1 tablespoon sour cream mixture.