Ingredients

• 1 (28-ounce) can whole peeled tomatoes
• ¾ cup chicken or vegetable broth, plus more as needed
• 1 large yellow onion, coarsely chopped
• 4 tablespoons unsalted butter
• 1 ½ teaspoons dried oregano
• 1 teaspoon granulated sugar
• Salt and black pepper
• Mayonnaise
• 8 slices brioche or milk bread, crusts removed
• 1 cup shredded low-moisture mozzarella (4 ounces)
• ¼ teaspoon dried oregano
• 2 tablespoons unsalted butter

Steps

1. Make the soup - Dump the canned tomatoes and their juices into a medium pot and using your hands, tear into coarse chunks. Swish the broth in the empty tomato can and add to the pot.
2. Stir in the onion, butter, oregano and sugar and season generously with salt and pepper. Turn the heat to high and bring to a simmer. Reduce the heat to medium-low, cover and continue simmering, stirring occasionally, until the onion is tender and the tomatoes have broken down, 15 to 20 minutes.
3. Meanwhile, make the sandwiches - Spread a thin layer of mayonnaise on one side of each slice of bread and evenly sprinkle the cheese and a little oregano on the mayonnaise side of 4 slices. Top with the cheeseless slices, mayonnaise-side down.
4. Melt 1 tablespoon butter in a large skillet over medium. Add the sandwiches and cook until golden brown on the bottoms, 2 to 3 minutes. Melt the remaining tablespoon of butter in the pan, then flip the sandwiches with a spatula, move them around to coat with the butter and cook until the other side is golden brown and the cheese is melted, 1 to 2 minutes. Turn heat to lowest setting to keep sandwiches warm.
5. Carefully purée the tomato soup using a blender until smooth and creamy, adding more broth if needed to loosen to your desired consistency. Season with salt and pepper. Transfer the grilled cheeses to a cutting board and cut each in half diagonally. Serve alongside the soup.