Sous vide barbecue beef sirloin, grilled onions and caramelised onion broth

Preheat a water bath to 65°C

Begin by preparing the onion broth. Peel and slice the onions horizontally into 1 inch thick pieces, then brush the slices with oil on both sides and lightly season with salt

Place a pan over a low heat, add the onion slices and allow to slowly caramelise until deep brown in colour. Once the onions are sufficiently coloured turn them over and repeat the process until the slices are evenly caramelised on both sides

In a separate pan, combine the water and stock and bring up to a gentle simmer, then add the caramelised onions. Continue to simmer the broth mixture until the liquid has thickened and reduced, taking on a strong flavour of onions – there should be roughly 400ml of liquid remaining in the pan

Strain the broth through a fine sieve and leave to cool, then add the kuzu and return the pan to the heat. Bring the onion broth back to the boil and allow the liquid to thicken, adjusting the seasoning to taste. Set aside, keeping warm until ready to serve

To cook the beef, season well and vacuum fully in a bag. Place the bag into the water bath to cook for approximately 35 minutes, or until the core temperature reads 55°C when checked with a needle probe

Meanwhile, prepare the grelot onions. Bring a large pan of salted water to the boil and add the onions, simmering for 2–3 minutes until the onions are soft. Remove from the pan and set to one side

Remove the beef sirloin from the bag and brush it with the kecap manis. Place the beef on a hot barbecue or grill and cook on each side for 4 minutes. Toss the grelot onions in olive oil and grill alongside the beef until evenly coloured

To serve, divide the broth evenly between four bowls. Carve the beef into four pieces and place into the broth along with the chargrilled grelot onions