Preheat the oven to 160°C (320°F). Scatter the salt on a baking tray, top with the potatoes and roast in the oven for 50 minutes.
To prepare the brussels sprouts, cut the core out of each with a small, sharp knife and break each sprout up into separate leaves. Set aside.
For the sofrito, in a non-stick pan over a low heat, add the oil and cook the capsicum, garlic and onion, stirring occasionally, for about 35 minutes. The idea here is not to get colour, but to soften the vegetables. Once soft, mix in the paprika and cumin to create a vibrant red glow. Keep it warm over a very low heat.
When the potatoes are nearly done roasting, in a saucepan gently warm the milk and butter. Remove from the heat. Remove the potatoes from the oven and, while still hot, remove the skin by putting the potato in a clean dish towel (tea towel) in one hand and peeling the skin off with a small knife. Force the potatoes through a potato ricer. Add the potatoes to the warmed milk and whisk; it should be runny. Mash this mixture together as best as possible, then pass through a strainer to make sure it's smooth. Season with salt and return to the saucepan and cover. You can keep it over a very low heat so it stays hot, but if you work reasonably quickly it will stay hot if you just cover it.
Get a cast-iron pan, wok or griddle extremely hot, add the oil and quickly cook the brussels sprout leaves, trying to burn the edges, then set aside on paper towel.
Bring a large saucepan of water to the boil with the vinegar, then crack the eggs in and lower to a simmer for 3 minutes. Remove the eggs with a slotted spoon and set aside.
To serve, put a generous dollop of hot mashed potato on each plate and place an egg in the middle. Toss the brussels sprouts in the sofrito and put to the side of the egg. Let the yolk crack and run for colour, squeeze the lemon juice over it and enjoy.