Add butter to the bottom of your slow cooker and turn it on high. In a few minutes, the butter will melt. At this point, add the onions and cherry tomatoes and toss to coat in the butter. Let this mixture cook for one hour on high.
Carefully remove the lid of your slow cooker and add to it the crushed tomatoes and stock. Cover and cook either on HIGH for 3-4 hours or on LOW for 6-8 hours.
Let soup cool slightly, then blend until smooth in your blender. Return soup to slow cooker.
Stir in cream cheese and put the top back on the slow cooker for another 10-15 minutes, or until the cream cheese has melted in. Season as needed.
Fill bread slices with Singles, spread outside of sandwich with butter. Cook in skillet on medium heat 3 min. on each side or until Singles are melted and sandwich is golden brown on both sides. Cut into quarters.
Serve soup with Grilled Cheese Croutons!