Heat a frying pan over medium-high heat, then coat the topside beef roasting joint in vegetable oil and season it generously with sea salt. Sear the beef for about 4-5 minutes on each side until a golden crust forms. Add the halved garlic bulb and onions to the pan in the last few minutes, letting them brown slightly for extra flavor.

Carefully transfer the seared beef along with the caramelized garlic and onions into your slow cooker. Pour in 500 ml of beef stock, scraping the browned bits from the pan to incorporate all the flavors. Whisk together 1 tablespoon of brown miso paste and 1 tablespoon of tomato purée, then add this mixture to the slow cooker for depth and richness.

Sprinkle 1 teaspoon of black peppercorns, 3 whole bay leaves, and 2 sprigs of rosemary into the slow cooker, ensuring they distribute evenly around the beef. Cover the slow cooker with its lid, and set it to cook on high for 1.5 to 1.7 hours, or on low for 2.3 hours until the beef reaches an internal temperature of 60°C (140°F) for optimal tenderness.

Once cooked, carefully remove the beef from the slow cooker and place it onto a plate. Cover it loosely with foil and let it rest for 30 to 40 minutes.

Strain the cooking liquid from the slow cooker into a jug, pressing the onions to extract maximum flavor, and skim off any excess fat from the surface.

In a small bowl, mix 2 tablespoons of cornflour with 4 tablespoons of the strained cooking liquid until smooth. Stir this mixture back into the slow cooker, and cook on high for an additional 10 to 15 minutes until the gravy has thickened.

Slice the rested Savory Slow-Cooker Roast Beef against the grain and serve it with the glossy gravy drizzled over the top.