Sift all dry ingredients, except pecans, together into a large bowl. In a separate bowl combine well the egg yolks, butter, Kahlua and milk. Whisk milk mixture into the flour and beat until smooth. Let batter rest for about 30 minutes. Beat egg whites until stiff, not dry. Fold egg whites, along with pecans, gently into batter. Bake according to directions on your waffle iron.