Combine white sugar, brown sugar and cream in a large saucepan. Cook slowly, stirring constantly, for at least 15 minutes, until a soft ball forms in a cup of cold water. Add pecans and cook a little longer, stirring constantly. Remove from heat. Add butter, vanilla and salt; beat until mixture looks sugary around edges of the pan. To speed the process, put the saucepan in cold water. Place wax paper on wooden or metal surface. Drop candy from spoon onto wax paper. If pralines “run” when dropped on paper and do not set, they have not been cooked long enough. Scoop up candy, cook a little longer, beat and try again. Let cool before removing from wax paper. Yield: 3 dozen pralines