Prepare the Beef Shank: Season the beef shank generously with salt and pepper on both sides.
Sauté the Vegetables: Set your Instant Pot to 'Sauté' mode and add the olive oil. Once hot, add the diced onion, garlic, carrots, and celery. Cook until softened, about 5 minutes.
Brown the Beef: Push the vegetables to the sides and place the beef shank in the center. Sear each side for about 3-4 minutes until browned.
Deglaze the Pot: Add the red wine to the pot, if using, to deglaze, scraping up any brown bits. Let it simmer for a minute.
Add Remaining Ingredients: Stir in the tomato paste, diced tomatoes, beef broth, thyme, rosemary, and bay leaf. Place the beef shank back into the pot, ensuring it's mostly submerged in the liquid.
Pressure Cook: Secure the lid on the Instant Pot and set it to 'Pressure Cook' on high for 50 minutes. Once the cooking time is up, let the pressure release naturally for 10 minutes before doing a quick release.
Serve: Carefully remove the beef shank from the pot. Serve it with the cooked vegetables and a ladle of the flavorful broth. Enjoy!