Boil the vegetable stock

Pour 2/3 of the olive oil into a nonstick pan (multiple small ones are better than a big one). Add the onion and cook for 5 minutes, stirring often, until it has softened but not colored. Stir in the tomato paste and sugar and cook for 1 minute. Add the tomatoes, some salt, and some black pepper, and cook for 3 minutes.

Meanwhile, put the couscous in a shallow bowl, pour over the boiling stock, and cover with plastic wrap. Set aside for 10 minutes, then remove the cover and fluff the couscous with a fork. Add the tomato sauce and stir well.

Wipe the pan clean and heat the butter and the remaining olive oil (1/3 of total) over medium heat. When the butter has melted, spoon the couscous into the pan and use the back of the spoon to pat it down gently so it is all packed in snugly. Cover the pan, reduce the heat to its lowest setting, and allow the couscous to steam for 10 to 12 minutes, until you can see a light brown color around the edges. Use an offset spatula or a knife to help you peer between the edge of the couscous and the side of the pan: you want a really crisp edge all over the base and sides.

Invert a large plate on top of the pan and quickly invert the pan and plate together, releasing the couscous onto the plate. Serve warm or at room temperature.