Rinse and drain the couscous and tip into a bowl. Add the salt then pour in the water. Allow to stand for 10 minutes or until the couscous has absorbed the water.
Add the oil and rub into the couscous grains with your fingers, then transfer the couscous to an ovenproof dish.
Dot the top with the butter and cover with a sheet of foil. Bake for 15 minutes to heat through.