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How to Cook a Thick-Cut Bone-In Sirloin Steak (18oz +)

A thick-cut bone-in sirloin steak is a true centrepiece, combining the depth of flavour from dry-aged beef with the succulence that comes from being cooked on the bone. At over 18oz, this steak demands a little patience and attention to technique — searing for flavour, resting for tenderness, and carving with respect for the cut. This guide ensures your steak is cooked perfectly, whether you prefer it medium-rare or cooked a touch further.

INGREDIENTS
  • 1 thick-cut bone-in sirloin steak (500g / 18oz +)
  • 1 tbsp beef dripping or neutral oil
  • 2 garlic cloves, lightly crushed
  • 2 sprigs fresh thyme or rosemary
  • 40g butter
  • Sea salt flakes
  • Freshly cracked black pepper
METHOD

  1. Preparation: Remove the steak from the fridge 1 hour before cooking to come to room temperature. Pat dry with kitchen paper.
  2. Seasoning: Generously season with sea salt and black pepper on both sides.
  3. Sear: Heat a heavy cast iron pan until smoking hot (or prepare a BBQ/grill with high direct heat). Add the dripping/oil and lay the steak in the pan, fat side down first to render.
  4. Caramelise: Sear each side for 2–3 minutes until a rich crust forms.
  5. Flavouring: Add butter, garlic, and thyme/rosemary to the pan. Tilt the pan and spoon the foaming butter over the steak for 1–2 minutes.
  6. Cook Through: For thick cuts, lower the heat or move to indirect heat (on the BBQ) and cook to your desired doneness (see below).
    • Rare: 50–52°C
    • Medium-rare: 54–56°C
    • Medium: 58–60°C
    • Medium-well: 63–65°C
  7. Resting: Transfer to a warm plate, loosely tent with foil, and rest for 10 minutes before carving.

Multi-Cooker Option (Ninja Foodi MAX)

  • Use the Sear/Sauté function to caramelise the steak with dripping and seasoning.
  • Switch to Bake/Roast at 180°C with a little stock or dripping at the base. Cook until the centre reaches your desired doneness (54–56°C for medium-rare).
  • Rest for at least 10 minutes before slicing.

Sides

  • Buttered greens with garlic – simple spinach or spring greens finished with butter.
  • Triple-cooked chips – crunchy, fluffy, the ultimate steak partner.
  • Pommes purée – silky smooth mash with extra butter.
  • Roasted heritage carrots with cumin – adds sweetness and spice.
  • Grilled field mushrooms – meaty, earthy, and satisfying.
  • Yorkshire salad – lettuce, cucumber, and vinegar dressing; a nod to tradition.

Matches

  • Black pepper, Dijon mustard, horseradish
  • Béarnaise or peppercorn sauce
  • Mushrooms, onions, shallots
  • Potatoes (any style), root vegetables
  • Red wine reductions or bone marrow butter

Preparation Time: 10 minutes (plus 1 hour bringing steak to room temperature).
Cooking Time: 15–20 minutes (including resting).

Hot Tips

  • Always bring a thick steak to room temperature before cooking to avoid uneven doneness.
  • Use a digital thermometer — guessing will let you down with a cut this size.
  • Resting is essential; the bigger the steak, the longer it needs to relax.
  • Carve against the grain for maximum tenderness.