Heat the olive oil and butter in a large heavy sauce pan over a moderate heat and when the butter is foaming fry the smoked bacon and onions for about 5 minutes or until the bacon is golden brown and the onions have soffend.
Add the garlic, bay leaf, thyme, carrots and celery and continue to fry gently for about 5-6 minutes, stirring occasionally until the vegetables have soften.
Add the chopped tomatoes, sugar and tomato puree, season with salt and freshly ground black pepper. Continue to cook for a few minutes and then add the passata and stock.
Bring to the boil, partially cover with a lid, reduce the heat to a simmer and cook gently for 25-30 minutes or until all vegetables are tender and the soup has reduced slightly.
Remove the bay leaf and sprig of fresh thyme and transfer the soup to a food processor or blend until smooth in a hand held blender. Return the soup into a clean saucepan and adjust the seasoning as required. For a really smooth soup, pass the soup through a fine sieve. Stir in the cream and sherry and ladle into warm bowls or mugs and serve with fresh crusty bread and butter