Heat the butter and oil together in a large stockpot over medium high heat.
Once the butter has melted, add the onions. Sauté for 2 minutes. Add the garlic and sauté for 1-3 additional minutes until the onion is softened.
Add the wine and cook approximately 4-6 minutes. Decrease the heat to low.
Stir in the flour and dry mustard. Cook for two minutes to get rid of the raw taste of the flour.
Gradually add the chicken stock, stirring constantly to prevent lumps.
Add the tomatoes, thyme, tomato paste and sugar.
Bring the soup to a boil, then reduce the heat a simmer, cover and simmer for for 15 minutes.
Remove and discard the thyme bundle if used. Puree the soup using a blender until smooth.
At this point the soup can be eaten as is. However, for a creamier texture, strain the soup through a mesh colander or food mill. Discard the solids left in the colander. Return the soup to the pot.
Add the cream and heat through.
Season with salt and pepper to your preference.