Usually, I agree with Nigella Lawson – “There is nothing worse than going out for Christmas lunch and finding someone’s done something interesting,” she wrote for Vogue in 1995. The same should be true for some other rarefied foods too, I tell myself. Brownies, roast dinners, cottage pies, and Yorkshire puddings... why mess with perfection?Still, if there’s one woman I might just trust to prove me wrong, it’s Mary Berry. That’s a good policy, seeing as the former Great British Bake-Off host loves to chuck wildcard ingredients into everything from her spag bol to her lasagne.Her cottage pie is no exception ― the Cordon Bleu-trained chef prefers not to use mash on its top, it seems.