For the Beef Tongue

1. Soak the beef tongue in salt water for 1 hour to remove impurities.
2. Add the tongue to a pot of fresh water and bring to a boil. Simmer for 15 minutes, then discard the water to remove scum.
3. Fill a clean pot with fresh hot water and add the tongue along with the onion, carrot, garlic, rosemary, thyme, bay leaves, salt, and black peppercorns. Bring to a boil, then lower the heat and simmer for 2 ½ hours.
4. Remove the tongue from the pot and let it cool slightly before peeling off the skin.
5. Slice the tongue into 1 cm (½ inch) thick slices.
6. Heat the cooking oil and butter in a pan over medium-high heat. Sear the beef tongue slices until golden brown on both sides.
7. Serve with the mashed potatoes and sauce.

For the Mashed Potatoes

1. Preheat the oven to 150°C (300°F).
2. Poke holes all over the potatoes with a fork. Drizzle with cooking oil, season with salt and black pepper, and rub to coat evenly.
3. Bake for 2 ½ hours, or until soft.
4. Let the potatoes cool slightly, then cut them in half and scoop out the flesh, discarding the skins.
5. Mash the potatoes using a ricer or potato masher.
6. In a pot over low heat, mix the mashed potatoes with butter and heavy cream, adding as much as needed to reach your desired consistency.

For the Sauce

1. In a dry pan over medium heat, sear the bacon with the rosemary until it starts to brown.
2. Add the shallot and cook for a few minutes. Stir in the sun-dried tomatoes and cook for another couple of minutes.
3. Sprinkle in the flour, stirring continuously, and cook for 2-3 minutes to remove the raw flour taste.
4. Pour in the red wine and let it reduce by ⅓. Season with salt and black pepper.
5. Add the veal stock and let the sauce simmer until it thickens to your preference.
6. Strain the sauce through a fine-mesh strainer.
7. Off the heat, stir in the butter to finish.