Peel and pit the avocados and in a blender blend them with the lemon juice, the sour cream, 3 cups of the broth, and the Tabasco until the mixture is smooth, adding enough of the remaining 1/2 cup broth to thin the mixture to the desired consistency.
Transfer the soup to a bowl, season it with salt and pepper, and chill it, its surface covered with plastic wrap, for 1 hour, or until it is cold. (The soup will discolor if kept for more than 6 hours.)
Stir half the salmon, chopped, into the soup, divide the soup among chilled bowls, and garnish it with the remaining salmon, cut into strips.
