Spread the semolina in an oven dish and add the coarsely chopped walnuts to it. Put it to crisp in a preheated oven at 338°F (170°C) till it turns rosy and the walnuts start browning.
Shake the oven dish continuously during baking. In the meantime, melt the butter on the stove and add the sugar and 4 cups of water to prepare the sugar syrup. Remove the browned semolina from the oven and put it on the stove on medium.
Pour the sugar syrup over it, while stirring. Reduce the heat and stir until there's no longer any liquid, being careful not to burn it. You need patience, because drying the semolina takes about an hour with constant stirring.
Finally, it will obtain the loose texture of sand. Remove the oven dish from the heat and cover with a towel for 30 minutes.