Soak beans overnight in a large bowl covered with 8½ cups cold water. Transfer beans to a large pot and add water to cover by 2 inches. Add garlic, bay leaves, halved onion, a couple of the dried mushrooms and a few pinches of salt. Cover with parchment paper so everything stays under water.

Simmer over low heat until beans are soft and creamy but still keep their shape, 1-1½ hours. Do not drain (there should be a fair amount of bean water). Fish out and compost onion halves.

Add potatoes and a generous pinch of salt. Cook until potatoes are cooked through and crushable, 10-15 minutes. Taste broth for salt: Make sure it is properly seasoned, or the end dish will taste underwhelming. Add kale and chestnuts, if using, and switch off heat. Preheat oven to 475 degrees.

Meanwhile, wash and trim squash, cut it in half, scoop out seeds and slice into 1-inch wedges. Place on a parchment lined baking sheet and sprinkle with a little vegetable oil and salt. Bake until a little charred and cooked through but still firm, about 25 minutes.

Chop remaining onion. Heat 2 tablespoons olive oil in a small frying pan and sweat onion with a pinch of salt over low heat, 10 minutes.

Use a mortar and pestle or food processor to pound remaining dried mushrooms into a rough powder. (You don’t want a fine powder, so don’t overdo it.) Add crushed mushrooms to pan with onions and cook, stirring, until sticky, 2-4 minutes. If the pan looks dry, add a few tablespoons of bean-cooking water. Season generously with pepper. Add herbs to bean pot.

Stir onion-mushroom mixture into beans, taste for seasoning, and reheat. Add squash and another pinch of chopped herbs on top. Serve with a drizzle of olive oil, a splash of vinegar or brine, sour cream or crème fraîche, and plenty of crusty bread.