In a medium soup pot, on medium heat, saute the leeks and onions in the olive oil and butter until the onions are translucent for about 10 minutes. Stir in the zucchini, salt, pepper, garlic, rosmary, tyme and the bay leaves. Saute for 10 more minutes, until the zucchini is tender. Add wine, then turn heat up to medium-high and cook about 1 minute, until liquid is cooked off. Remove half of the vegetables and set aside.
Sprinkle the flour into the remaing half of the vegtables, stirring, until the vegetables are well coated. Add the stock. Heat, stirring frequently, until the soup begins to thicken. Remove it from the heat. When the soup has cooled a little, puree it in a blender or food processor and return it to the pot.
Add the reserved vegetables and heat the soup to simmering. Stir in the cream . Do not let the soup boil.