Prepare the meatball mixture: In a large bowl, combine the minced beef, beaten egg, breadcrumbs, grated onion, minced garlic, salt, pepper, and smoked paprika. Use your hands to mix gently until everything is just incorporated — you want the mixture to feel soft and slightly sticky, but not overworked.

Shape the meatballs: Roll the mixture into walnut-sized balls, about 2.5 cm in diameter. Place them on a baking tray lined with parchment. You should have roughly 30–35 meatballs. The surface should feel smooth and uniform, with no cracks.

Brown the meatballs (optional but recommended): Heat a large frying pan over medium-high heat with a splash of neutral oil. Working in batches, sear the meatballs for 2–3 minutes, turning occasionally, until they develop a deep golden-brown crust. You'll hear a satisfying sizzle, and the kitchen will fill with a toasty, savoury aroma.

Make the sauce: In a medium bowl, whisk together the ketchup, honey, apple cider vinegar, Worcestershire sauce, and soy sauce. The mixture should be a vibrant reddish-amber colour, with the honey making it slightly thick and glossy.

Combine in the slow cooker: Place the browned meatballs into the crockpot in a single layer if possible. Pour the sauce over the top, gently turning the meatballs to coat them evenly. The meatballs should be mostly submerged in the sauce, which will look thin now but will thicken as it cooks.

Cook low and slow: Cover the slow cooker and set it to low heat. Cook for 3–4 hours. After about 2 hours, the sauce will start to bubble gently around the edges, and the meatballs will release a sweet, smoky fragrance. Stir once halfway through to redistribute the sauce.

Thicken the sauce (optional): About 30 minutes before serving, stir in the cornflour slurry. Let it cook uncovered for the final 30 minutes. The sauce will visibly thicken, turning into a rich, sticky glaze that clings to each meatball. The colour will deepen to a dark mahogany.

Serve: Transfer the meatballs to a serving dish, spooning extra sauce over the top. Garnish with chopped spring onions or sesame seeds if desired. The meatballs should be tender enough to cut with a fork, and the sauce should coat them like a shiny, sweet-tangy shell.