Saute peppers, onion, and tomato in olive oil until soft, then add in tomato paste, cilantro, and garlic to make a sofrito. Cook until soft and caramelized, at least 10 minutes.
In food processor, grind the malanga and bananas with the milk, and then add the sofrito. Continue to grind until very smooth. Add cornstarch and mix until fully incorporated. Season, to taste, with salt and pepper.
Cut banana leaves into 4 (8 by 11-inch) pieces. Place a spoonful of this mixture into the middle of the banana leaf and then divide the olives, raisins, and ham into equal parts and place these on top of the pasteles. Wrap like an envelope and tie with a string. Boil for 45 minutes.