Stir up Sunday: who makes the best Christmas puddings? The Ultimate Plum Pudding Company is run by partners (both in life and business) Carole Taylor and Bernice Humphreys. Taylor, a no-nonsense woman with an acerbic Northern sense of humour, shows us into the factory, where a dustbin-sized Fifties Hobart mixer - like a giant KitchenAid - was being readied for the production of the new puddings. "We're only making 1,000 of Fortnum's Nuts About Christmas pudding," she tells me. It's going to take eight people three days. We can usually do 1,500 in a day. The idea of the butter centre was operations manager Nicola Smith's, Taylor says with a twinkle. And if she ever has another one like it she's sacked. A heady scent of molasses wafts up as a tub full of dark muscovado sugar hits the Hobart's beaters, followed by spices (I detect nutmeg and clove), flour and breadcrumbs. "We mix it well now," explains Smith, who used to work as a chef for Claridge's and the Savoy, "or the sugar stays in clumps that liquefy when the pudding is cooked." Next, the Italian candied peel and Australian candied ginger are tumbled in and stirred up again. "You need everything to get a good coating of flour or they will drop to the bottom, leaving the cake mixture at the top," Smith says. They are so syrupy they can just slide through. Then there is beef suet (vegetarians look away - but it really does make for a better texture) and damsons from the nearby Lyth valley. The order of addition is important. "Add the liquid too early and you make a heavier pud," says Smith. But now the free-range eggs can be mixed in, along with finely grated lemon zest, damson purée and Kentish cobnuts. Finally, in goes the dried fruit, already soaked in Somerset cider brandy for 48 hours, and the beaters turn for five minutes, filling the room with a heady boozy smell. To one side of the room a team of three are carefully arranging the walnut and cobnut topping in the base of china eau-de-nil pudding basins, before spooning in the pudding mix. Now it is time for the key part, the brandy butter filling. The butter has already been scooped and frozen, before being wrapped in a layer of marzipan, a job done by Taylor and Smith. It was our job every Thursday afternoon for weeks. We got a lot of gossiping done," laughs Taylor. The trick is to squeeze the marzipan around and finish it to make a perfect seal so that the butter doesn't leak out. When the butter and marzipan ball is nestled in to the pudding mixture, the bowl is covered and put with the others ready to be steamed for three and a half hours at 90C. This is a lower temperature than a home cook might expect, but Smith insists: "If a pudding gets too hot the fat seeps out of the mix, which makes for a heavy pudding and claggy feeling in the mouth." The puddings are cooled and hand-fed with cider brandy before being topped with the traditional cloth, ready for a final steaming at home. Or microwave? If you do that, you cook it from the inside out and lose the juiciness of the fruit. And it's very easy to overcook and wreck it," Taylor tells me firmly. Nicola, pragmatically, adds, "If you are going to use a microwave, then we recommend doing it on defrost." I fancy that is one shortcut that isn't worth taking. Sussex Pond Christmas pudding recipe Fortnum and Mason's "Nuts About Christmas" pudding costs £40 and serves 6-8 (fortnumandmason.com). One pudding will come with a gold sovereign worth £200