No one is doubting the glory of mashed potatoes, and while they are not difficult to make, they can be quite a faff in large quantities at the last minute. This is the answer: a tangy, subtly cheesy mash, with a crunchy topping, that has revolutionized my cooking life. I made them for the first time last year for Thanksgiving, and they have happily appeared on my table several times since. They come heartily recommended with the Slow-Cooked Black Treacle Ham, and any time you want to spread…