1. In a large bowl, mix the flour and 1/4 cup chicken stock and gently mix together till smooth.
2. Add this stock to the remaining chicken stock in large saucepan and bring to a boil, while stirring constantly. When thickened, remove from heat.
3. Peel, deseed and mash the meat from the avocados and add this mixture to the stock mixture to blend thoroughly. Set aside to chill. Stir in cream and pepper just before serving.