How to Make It
Place potatoes and bay leaf in a large saucepan; add water to cover by 2 inches. Bring to a boil over high; reduce heat to medium, and simmer until tender, 23 to 25 minutes. Drain well in a colander; discard bay leaf. Return potatoes to pot. While still very hot, mash potatoes to a smooth consistency. Stir in butter and salt using a potato masher or whisk.
While potatoes boil, microwave cheese and tomatoes in a large microwavable bowl on HIGH 3 minutes. Stir well. Continue microwaving on HIGH until cheese is melted, 30 to 60 seconds. Stir until smooth.
Swirl cheese mixture into mashed potatoes; serve immediately.