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1
Place the pork ribs or lacón in a large pot and cover generously with cold water. Bring slowly from cold to a gentle simmer — not a rolling boil. A clean, pale broth will rise; skim off any grey foam that forms on the surface. The broth is ready to proceed when it runs clear and smells sweet rather than raw.
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2
Add the drained soaked beans to the pot with the pork and its broth. Maintain a steady, gentle simmer. Cook until the beans are tender throughout but still holding their shape — press one between finger and thumb; it should yield completely with no chalky centre. This will take the greater part of the cooking time.
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3
Add the potatoes, broken into rough chunks. Breaking rather than cutting releases their starch directly into the broth, thickening it to a body that is still thin but no longer watery. Cook until the potatoes are completely soft and beginning to dissolve at their edges — the broth will turn faintly opaque and coat a spoon lightly. This is where the dish lives or dies: a broth too thin is unfinished; a broth too thick has lost the character of caldo. Adjust by mashing a few potato pieces against the side of the pot if the body is insufficient.
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4
Add the grelos no earlier than 15 minutes before serving. Press them beneath the surface of the broth. They must remain al dente — bright in colour and with perceptible resistance when a stem is bitten. Collapsed, grey greens indicate over-cooking and the loss of the bitterness that defines the dish.
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5
Season with salt only now, tasting carefully: the pork — particularly lacón — will have released significant salt during the long braise. Add in small increments, tasting between each addition, until the broth is savoury and the bitterness of the grelos is in balance with the fat of the pork.