1 To make a cartouche, cut a square or round greaseproof paper and fold into segments, the shape of an elongated triangle. Trim the triangle to a fraction larger than the radius of your pan.

2 Unfold the paper into a circle that should fit snugly inside the saucepan on top of the onions.

3 Crumple the cartouche and dampen under cold water before use. The crumpling helps the greaseproof paper hold a little more water. Lay on top of the ingredient(s) to be cooked.