Heat a large, heavy-based saucepan over a medium to high heat. When the pan is hot, add the tomatoes and fry for 4-5 minutes, or until they have started to break down.
Add the garlic, basil, tomato purée and two tablespoons of olive oil. Continue to cook for a further 1-2 minutes.
Pour in the vegetable stock, bring the mixture to the boil, then reduce the heat until the mixture is simmering. Simmer for 3-4 minutes.
Transfer the soup mixture to a food processor and blend to a purée.
Return the blended soup to the pan and season, to taste, with salt, freshly ground black pepper and sugar.
Pour in the cream and return the mixture to a simmer. Continue to simmer for a further 1-2 minutes.
Meanwhile, brush the ciabatta slices with the remaining two tablespoons of olive oil.
Heat a griddle pan until hot, add the ciabatta slices, in batches if necessary, and cook for 1-2 minutes on each side, or until golden brown griddle marks appear on both sides of the ciabatta.
To serve, ladle the soup into four serving bowls. Drizzle a swirl of double cream into each bowl, then a swirl of olive oil, to garnish. Sprinkle over a few basil leaves.