Boil the tongue in plenty of boiling water for about 20–30 minutes, depending on the tenderness of the cut. Drain and set aside.
In a skillet, add the sliced onions and a drizzle of extra virgin olive oil.
Cook over low heat until the onions have softened and wilted.
Cut the parboiled tongue into bite-sized chunks or thin slices. Add it to the pan along with salt and chili pepper to taste, then continue cooking until the onions break down almost completely into a rich, creamy sauce.
Add a splash of water as needed during cooking to keep the mixture moist.