In a wide frying pan, fry the onion, garlic and herb stems over a medium heat in 1 tablespoon of the butter with a good pinch of salt (less if your leftover quinoa has already been seasoned), pepper and chilli for 5 minutes, stirring from time to time.
Meanwhile, whisk the eggs in a large bowl, then mix in the flour, followed by the cold quinoa and crumbled feta. Add the garlic, onion and herb mix to the bowl with the herb leaves. Mix well and shape into 12 cakes (or 24 bite-size), about 1cm thick. The easiest way to do this is to split the mix into two, and then keep dividing. If you’re finding it tricky to form them, try adding a touch more flour.
If the cakes feel firm, then go ahead and start frying them. If not, pop them onto a plate and into the fridge to firm up for 15 minutes. Use this time to make the chimi- churri yoghurt by combining all the ingredients with some salt and pepper and blitz- ing in a food processor. Or you can chop all the ingredients, then thin it out with a few tablespoons of water if you like it saucier.
Heat 1 tablespoon of butter in the original pan then, once hot, add however many cakes you can fit into a single layer – I could fit four in my pan. You don’t want them to be touching or they’ll steam instead of fry. Let them sizzle for about 3 minutes on each side to get nice and golden and hot throughout. Then repeat for the rest of the batch. I turn the heat up as I add the cakes, then lower to a medium heat to fry. Put your cooked cakes in a low oven to keep warm while you finish the rest.