
Heat the remaining oil and knob of butter in a large, nonstick frying pan. Keep warm, but don't overheat it or the sauce will split. Whisk into the sauce and simmer for 1-2 minutes. Mix the teaspoon of butter with the flour into a smooth paste. Put the vegetable or chicken stock, wine, double cream and the 25g butter into a medium-sized saucepan, bring to the boil and bubble rapidly for 7-8 minutes until it has reduced by about three-quarters and is the consistency of single cream. Shape the mixture into 4 discs, about 2.5cm thick chill for 1 hour. Mix the cooked leek, mashed potato, greens and seasoning in a bowl. Add the sliced leek and cook for 3 minutes, stirring until lightly browned. Heat ½ tablespoon of the olive oil in a small frying pan. If using greens, chop them into small pieces. If the potatoes aren't already mashed, mash them with the back of a fork into a coarse purée. Make sure both the potatoes and the greens are very dry, to ensure that the bubble and squeak cakes become crispy.

Make the sauce a few hours ahead reheat very gently. Top with salad leaves to finish.Make the bubble and squeak cakes up to a day ahead cover and chill.

If you’ve got any parsley or mustard sauce leftover, a drizzle of this on top really finishes the dish. This weekend, I’ve put a different spin on Ireland’s favourite meal, by making crispy browned Bubble and Squeak cakes out of the leftover spuds and cabbage, to make a bed for hot or cold bacon slices.
