The sweet chestnut (Castanea sativa) is the glossy, mahogany-brown nut of a great deciduous tree, the odd one out among nuts: where almonds, walnuts and pecans are oily and rich, the chestnut is starchy and low in fat, so it cooks soft and floury like a chestnut-coloured potato rather than crunchy and buttery. Roasted over coals it is the quintessential European winter street snack, all sweet, nutty steam; it is also boiled, candied into glossy marrons glacés, whipped into the chestnut-cream tower of Mont Blanc, milled into a sweet gluten-free flour, and folded into festive stuffings.