Preheat the Oven: – Preheat your oven to 325°F (160°C). Season and Sear the Lamb Shanks: – Season the lamb shanks generously with salt and black pepper. In a large, ovenproof Dutch oven or heavy-bottomed pot, heat the olive oil over medium-high heat. Add the lamb shanks and sear them until they are browned on all sides. This should take about 8-10 minutes. Remove the lamb shanks and set them aside. Sauté the Aromatics: – In the same pot, add the chopped onions, minced garlic, carrots, and celery. Sauté for about 5 minutes or until the vegetables start to soften and become fragrant. Add Herbs and Stout: – Tie the rosemary, thyme, and bay leaves together with kitchen twine to create a bouquet garni. Add this to the pot along with the tomato paste. Stir well to combine. Pour in the stout beer, scraping the bottom of the pot to release any flavorful bits. Bring the mixture to a simmer.