The kitchen window has fogged over. That's how you know the soup is doing what it should. There's a pan on the hob, leeks collapsed into butter, potatoes softening in stock, and the room smells of something so quietly good that it barely announces itself. This is not a soup that shouts. It arrives gently, like a hand on your shoulder.

Leeks and potatoes. I can't think of a more honest combination. The leeks bring sweetness, the potatoes give body, and the butter holds it all together. There's nothing to hide behind. No spice rack to raid, no clever technique to master. You soften, you simmer, you blend. A recipe is a conversation, not a contract, and this one barely needs a recipe at all. Once you've made it twice, you'll do it from memory.

I come back to this soup every autumn, usually the first week the evenings draw in properly and the kitchen feels like the warmest room in the house. I wrote it down in the notebook years ago, just a few words: leeks, butter, stock, Tuesday. The rain was heavy that evening. The soup was right. Sometimes that's all you need to record.

It's worth saying that this soup is equally good cold, thinned with a little extra stock and served in smaller bowls on a warm evening with chives snipped over the top. The French call it vichyssoise and serve it as though they invented something. We've been making it in this country for longer than anyone remembers. We just didn't give it a name.