Fish Cakes with Hollandaise Sauce

Delicious though mashed potatoes are, once they cool and enter the fridge they become riddled with some kind of curse. You will never reheat them to their original glory.
However, mashed potatoes are extensively useful as a leftover ingredient. You could make a loaf of hearty German potato bread, or, even better, fish cakes and (admittedly not really using leftovers) fresh hollandaise sauce- easier than you think.
1)There's no point providing a measurement for the mashed potato as they're leftover, but think about 2 cans for every 2 servings of mashed potato, which requires one egg to bind (so you can't use much less of either fish or potato) I use cat food heaven in the form of tinned salmon, but tuna would also be good. To help the mashed potato come back to life if you're just using plain old boiled potatoes then add a little melted butter and milk. To the mash and fish, season with plenty of salt and pepper, and add the zest of half a lemon, 2 finely chopped spring onions, a pinch of chilli powder (optional), 2 tbsp finely chopped parsley and about 2 tbsp capers. To work as a binding agent, add one egg. The mixture should be soft and sticky but you still need to be able to form it into patties.
2)(you guessed it) form the mixture into fairly small patties and leave in the fridge to firm up before cooking on a baking sheet that you lined with clingfilm before you started. I should tell you that I nearly always make 5 out of these for some reason, but this of course depends on how big you make them.
3)This is a good time to start the hollandaise. It sounds like a nightmarish task, cooking egg yolks over a pan of simmering water, and yes, I can't promise it will never curdle, but I can promise that provided you're vigilant, have an insistent but gentle heat under the eggs and prepare for overcooking by having a bowl of iced water beside for dipping, then your hollandaise will work. And if it still doesn't, then quietly discard it and have the fish cakes with ketchup- no one has to know. The worst thing you can do is attempt this fearfully; that's condemning the sauce to curdle before you begin. You need to start by infusing 2 tbsp white wine vinegar with some cheat shortcuts. Traditionally,  mace is used which is, I suppose, the shell of nutmeg; I can't get hold of it, so I use the old leavings of a nutmeg when they're too small to continue grating. Place it in a small pan with the vinegar, a few peppercorns, a bruised spring onion and a bay leaf. Heat gently until slightly reduced, then transfer to a heatproof bowl that contains 3 egg yolks (freeze the whites in a bag for meringue etc). Melt and cool 150g unsalted butter and transfer to a jug. Place the bowl over a pan of gently simmering water, but don't let the water touch the base of the bowl and start pouring the butter into the egg yolks, whisking constantly with a very slow stream just like mayonnaise. When most of it has been absorbed you can pour in the butter with a less delicate wrist. If the mixture splits, you may find upping the heat can help everything emulsify again, or it's too hot and needs to be dipped into a bowl of iced water. Remove from the heat when fully cooked, then add a very small squeeze of lemon that you zested before and a pinch of salt and white pepper. Set aside to come down to room temperature while you coat and cook the fish cakes.
4)You could use breadcrumbs or, even better, panko for this if you have them on hand, but if not coat the fishcakes in raw polenta. Fry them until crispy in a thin layer of oil to prevent burning. Serve with a crisp salad and the sauce.