First make a roux with the 3 tablespoons of flour and 4 tablespoons of olive oil added to a saute pan and cooked until it darkens. Make this roux first so that it will be cool when you are ready to add it to the soup.
Soak the olives in cold water for 1 hour (this helps to remove some of the salt). Drain and coarsely chop the olives. Heat a saute pan and add 3 tablespoons of oil, onion, and garlic, along with 2/3 of the olives. Saute until the onions are transparent. Puree the mixture in a food processor along with 1 cup of the stock. This much of the recipe can be made up to two days ahead if needed.
Place this mixture into a 4 quart saucepan and the rest of the stock. Simmer for 20 minutes and add cream. Whisk in the roux a little at a time and simmer, stirring constantly until thickened. Add pepper to taste and remaining chopped olives, Tabasco, and sherry.