Pupusas are thick corn cakes stuffed with cheese, beans or meat. In their home country of El Salvador they are a common sight on street carts or in the fabulously named pupuserías , the cafés dedicated to serving them. Curtido is a pickled slaw that gets better with time, so make it well ahead for the best possible flavour.
Note: you will need to begin this recipe the day before you want to eat, to allow the flavours of the curtido to develop.
Begin by making the curtido as it needs time to pickle – overnight is ideal, or for a minimum of 6 hours. It will keep in the fridge, maturing nicely, for at least a week, so you can make it well ahead if you want to. Stir together the cabbage, carrot and onion in a large bowl, and season with salt and pepper.
Add the coriander and cumin seeds to a small frying pan and toast over a medium heat for a minute or two. Tip into a spice mill or pestle and mortar and grind to a powder, then add to a saucepan along with the vinegar, 75ml water, sugar, oregano and chilli flakes. Set over a medium heat and bring to the boil, then pour this mix over the vegetables and stir thoroughly. Leave to pickle for as long as possible, stirring every now and then.
For the refried beans, toast the cumin seeds in a dry frying pan over a medium heat for a minute or two. Tip into a pestle and mortar and grind roughly. Pour the oil into the pan and set back over the heat. Once hot and reduced slightly, add the onion and fry for about 15 minutes until soft and lightly coloured. Stir through the garlic, crushed cumin seeds and chilli flakes, and season with salt and pepper. Fry for another minute before tipping in the beans. Cook for about 5minutes over a medium-low heat, crushing the beans with a potato masher as they heat through. Set aside to cool a little so you can handle them comfortably.
To make the pupusas , mix together the masa harina with a generous seasoning of salt and pepper in a bowl. Pour in the melted butter and enough warm water to form a crumbly dough when combined. Tip on to the worktop and knead briefly to bring it together in a ball. Divide into 8 pieces, weighing each for accuracy if you want to ensure even-sized pupusas . Take a piece of dough and roll it into a neat compact ball between your palms. Cupping it in one palm, press the thumb of your other hand firmly into the centre to make a hole. Then, working around, gradually enlarge the hole with your thumb and forefinger so you get a deep cup shape.
Supporting the cup in the palm of your hand, take a tablespoon of mozzarella and drop it into the middle. Then add a heaped teaspoon of refried beans on top, pressing it down with the back of the teaspoon. The trick is to get as much filling as possible inside but still be able to seal it up completely. Continue to cup in the palm of your hand as you use the other hand to pinch the sides to meet each other over the filling, completely sealing it in. Then cup in both hands and gently roll into a ball before slowly increasing the pressure, flattening the ball to a disc about 1.5cm thick. If you go slowly and carefully not too many cracks should appear, and if they do, simply push the edges back together. Repeat with the remaining pieces of dough. You will not need to use all the refried beans, but they will keep for 3–4 days in the fridge (and are fabulous spread on hot buttered toast!).
When you are ready to cook, add a good glug of vegetable oil to a large frying pan – you need a thin layer to cover the base. Set over a high heat and, once hot, fry the pupusas a few at a time for about 2 minutes on each side until crisp and golden. Remove from the pan and drain on kitchen paper. Repeat with the remaining pupusas , adding a little more oil if necessary. Top each with a little of the curtido and eat while still hot.