In the carafe of a high-powered blender, combine the black beans, mayonnaise, buttermilk, dill, ranch seasoning mix and black pepper. Blend on high speed until a thick dip forms, about 2 minutes. Store, refrigerated, in an airtight container until ready to serve.
Serve the dip in a bowl lined with gem lettuce leaves. Sprinkle with "soil" made from the pumpernickel crumbs. Serve alongside assorted crudites, such as cauliflower in various colors, sugar snap peas, cherry tomatoes on the vine, mini rainbow carrots with greens, celery sticks and endive.