Combine sugar & water in saucepan & stir occasionally until dissolved, over medium heat. Bring to a boil, & boil briskly for 5 minutes without stirring. Remove from heat & leave aside in pan. In a deep heavy pan heat ghee & add semolina. Stir over medium heat for 5 minutes. Semolina should not color.
Pour hot syrup into semolina, stirring constantly. When smoothly blended, reduce heat & leave to cook, uncovered, until liquid is absorbed. Mixture should be thick but still moist at this stage. Stir in nuts, cardamon & rosewater to taste.
Cover rim of pan with a cloth or 2 paper towels, put lid on tightly & leave on low heat for 5 minutes. Turn off heat & leave pan undisturbed for 10 minutes.
Spread halwau on a flat, lightly oiled platter & decorate with nuts. Serve warm or cold, cutting pieces into diamond shapes or squares.