I got into a conversation the other day about warming plates. Nowadays it’s automatic and I always do it. Before I cooked professionally, it was pretty rare – special occasions only, and then only if I remembered.Something else that mystified me was: When should you put a lid on saucepans? When boiling potatoes? When making soup? When browning onions for soup? When making stew? And if so, why? Or why not?In fact, all it takes is a little common sense, like so much in cooking. If you’re heating things up to cook them – boiling potatoes, making soup – then put the lid on. It reduces the cooking time and reduces the energy you need. If you’re trying to colour something, or reduce it down – caramelising onions for soup, or thickening a sauce – then leave the lid off to let the steam out. If you keep the lid on then, duh, it won’t reduce.