Peel and roughly chop 2 medium onions and 2 cloves garlic.
Thoroughly season 2 pounds pork loin roast with 2 teaspoons salt and ½ teaspoon ground black pepper on all sides. To ensure the pork holds its shape well during roasting, tie it with kitchen twine.
In an oven-safe roasting pan, heat 2 Tablespoons sunflower oil to a high temperature. Once the oil is hot, brown the roast on all sides. Set the seared meat aside on a plate.
Reduce the heat to medium. Add the chopped onion and garlic to the roasting pan with the browned bits and sauté for about five minutes, stirring constantly. If needed, add a little more fat or a tablespoon or two of water.
Preheat the oven to
300 °F, lower and upper heat. Place the roast over a bed of sautéed onions and garlic and add half ½ cup water. Roast uncovered in the preheated oven for an hour. When the roast is done, remove it from the pan and wrap it in a sheet of foil to rest.
Meanwhile, prepare a flavorful gravy with the onion, garlic, and drippings. Transfer the contents of the baking dish to a mixing bowl and blend briefly with an immersion blender. If too thick, add a few tablespoons of water. Pour the blended mixture through a sieve into a saucepan, pressing it through with a spoon to create a smooth gravy. Heat the gravy, taste, and adjust the seasoning with salt or pepper if needed.
Remove the pork from the foil. If there is any juice left in the foil, pour it into the gravy. Using a sharp knife, cut the roast into thin slices, about ⅓ inch (0.8 cm) thick.