Heat two tablespoons of oil into a non stick frying pan, on medium heat. Add the onion and saute for 5 minutes, stirring often, until softened, but not coloured.
Stir in tomato paste and sugar, and cook for 1 minutes. Add tomatoes 1/2 tsp salt and fresh ground pepper, and cook for another 3 minutes.
Meanwhile, pour the boiling water over the couscous in a shallow bowl and cover with plastic wrap. Let stand for 10 minutes. Fluff the couscous at the end of the 10 minutes, adding the tomatoe sauce mixture.
Clean the fryin pan and add the remaining 1 tablespoon of oil with butter, over medium heat. Add the couscous, once the butter has melted, and using the spatulas, flatten the couscous, and heat until a crisp edge develops over the base and sides.
Carefully invert the couscous onto a plate, by placing a plate over the top of the couscous, before inverting, releasing the couscous from the pan. Serve warm or at room temperature.