Preheat the oven to 180C. To make the bombas, spread the rock salt evenly over a baking tray and place the potatoes on top. The salt helps to draw out excess moisture from the potatoes. Bake for 45 minutes or until potatoes are cooked through.
Meanwhile, make the meat filling. Heat the oil in a large saucepan over medium heat and saute the onion and garlic for 6-8 minutes or until translucent. Peel the skin from the pork sausage and discard. Crumble the meat into the pan. Saute for 10 minutes.
Add the sherry and simmer until sherry has evaporated. Check the seasoning. Cool slightly, then transfer to a food processor and process to a coarse paste. Cool, cover and refrigerate until ready to use.
Allow cooked potatoes to cool, then peel. Mash the flesh with the olive oil until smooth. Season to taste.
Take 1 heaped tablespoon (about 45g) and roll into a ball. Poke your index finger halfway through the ball to make a hole. Fill the hole with about ½ tsp of the butifarra filling. Close the hole, roll into a smooth ball and place on a tray. Continue with remaining mash and filling. Cover the bombas with plastic wrap and refrigerate for one hour.
Meanwhile, make the salsa brava. Heat the oil in a medium pot over slow heat and saute the onion, the fresh chili and garlic for 30 minutes. Add the pimiento choricero meat, the paprikas and cook for 5 minutes. Add the vinegar and simmer until the vinegar has evaporated. Add the flour and cook the mixture for 3 minutes then add the chicken stock and bring it to the boil. Tranfer into a blender and blended until smooth. Pass through a fine sieve and set aside.
To make the aioli place the garlic cloves, the yolks and the lemon juice in a blender. Start blending the mix until we have a smooth paste. Then add the olive oil slowly while blending. This will allow the emulsion of all the ingredients.
To crumb the bombas, arrange three wide shallow bowls in a row. Place the flour in the first, the beaten egg in the second and the breadcrumbs in the third. Roll the bombas in the flour, dip in the egg, allowing the excess to drain off, then roll in the breadcrumbs, coating well, and place on a tray.
Fill a large heavy-based saucepan or deep-fryer one-third full with oil and heat to 170C or until the point when a cube of bread dropped into the oil takes 20 seconds to turn golden. Deep-fry the bombas, in batches, for 3-4 minutes or until golden all over and hot on the inside. Drain on paper towel.
To serve, spoon small dollops of salsa brava on to a serving plate, then place a bomba on top of each; the sauce will stop the bomba from slipping around. Garnish each with a dollop of the aioli and salsa brava and serve straight away.