Start the soup base: Heat the olive oil in a large stockpot over a medium heat. Add the diced onion and cook for 8–10 minutes, stirring occasionally, until the pieces turn translucent and begin to soften. You’ll notice a sweet, gentle aroma rising from the pot—that’s the sugar in the onions caramelising slowly.

Add the garlic and tomato purée: Stir in the minced garlic and tomato purée. Cook for 1 minute, until the garlic becomes fragrant and the purée darkens to a deep brick-red colour. The smell will shift from sweet to richly savoury.

Simmer the tomatoes: Pour in the tinned tomatoes, breaking them up with a wooden spoon. Add the chicken stock, dried basil, oregano, and sugar. Bring the mixture to a gentle boil, then reduce the heat to low. Let it simmer uncovered for 20 minutes. The sauce will thicken slightly, and the colour will become a deeper, more vibrant red. Stir occasionally to prevent sticking.

Blend until velvety: Remove the pot from the heat. Using an immersion blender, purée the soup until completely smooth. If you don’t have one, carefully transfer the soup to a blender in batches. The final texture should be silky, with no visible chunks. Stir in the double cream and season with salt and pepper. Keep the soup warm over a very low heat while you make the sandwiches.

Prepare the bread: Lay out the 8 slices of sourdough. Spread one side of each slice with the softened butter. Flip half the slices over so the buttered side faces down—these will be the bottoms of your sandwiches. Evenly distribute the grated cheese over these four slices, then top with the remaining four slices, buttered side facing up.

Grill the sandwiches: Heat a large frying pan or griddle over a medium-low heat. Place two sandwiches in the pan at a time—do not overcrowd. Cook for 3–4 minutes on the first side. You’ll hear a gentle sizzle, and the bottom should turn a deep golden brown. Press down lightly with a spatula once during cooking. Carefully flip and cook for another 3–4 minutes, until the second side is equally golden and the cheese has melted into a gooey, stringy layer. The crust should feel crisp and sound crunchy when you tap it.

Rest and serve: Transfer the sandwiches to a cutting board and let them rest for 1 minute. This allows the cheese to set slightly, so it doesn’t all ooze out when you cut the sandwich. Slice each sandwich in half diagonally and serve immediately with the warm tomato soup.