Using a sharp knife, peel the grapefruit, lemon and lime, removing the bitter white pith. Cut in between the membranes to release the citrus sections. In a medium skillet, melt the remaining stick of butter. Add the pecans and cook over moderate heat, stirring, until golden, about 6 minutes. Remove the skillet from the heat and add the Grand Marnier. Return the skillet to the heat and carefully ignite the liquid with a long match. When the flames subside, add the sugar and water mixture and boil until thickened, about 1 minute. Add the cream and salt and boil for 1 minute.