Turnip mash with greens, caramelised onions and feta

This started off as a way to use up all the turnip and potato flesh we’d generated from recipes in which turnips and potatoes were stuffed. The turnips made the cut, the potatoes did not. The resulting mash turned out so good, though, that it soon became a reason to buy the vegetables in the first place! Necessity (not to discard good food) was indeed the mother of great invention here (along with Noor, of course, our crucial right-hand lady on the book, w