A sirloin joint is the roasting version of the steak you already know. It has a fat cap, a tender eye, and it wants to be served pink, not grey. Sirloin Joint 1kg is a 1kg roast for a small table. Sirloin Joint 2-2.2kg (Frozen) is a frozen 2–2.2kg joint. The 4–5kg fresh whole sirloin is the cut-your-own piece. They live in sirloin joint and beef joints.
Roasting times
1kg sirloin: brown the fat cap in a pan, then 180°C for 35 to 45 minutes, probing 52–54°C for medium-rare. Rest 15 to 20 minutes. The frozen 2–2.2kg joint: defrost in the fridge 24 hours, then about 1 hour 10 minutes to 1 hour 20 minutes at 180°C, still to that same internal number, rest 20 minutes. Slice across, not with the grain. A sirloin joint without a rest is a puddle and a dry slice. That rest is not optional on a lean-ish roast.
The 4–5kg joint and cut-your-own
Fresh Whole Sirloin Joint 4-5kg can be roasted as a huge joint for a party, or sliced into 2–3cm steaks and treated as the sirloin steaks you already know how to pan-fry. If you roast the whole thing, 180°C, probe, and budget a long rest — 30 minutes. Shop cut your own steaks and Sunday roast depending on whether you are carving a roast or filling a freezer with steaks you cut yourself. Do not try to pan-fry a 4kg joint.
Sirloin joint versus topside
Topside is leaner and less forgiving. Sirloin has the fat cap that bastes as it cooks, which is why it is the nicer roast if you want pink slices that still taste of steak. Leftover sirloin joint is cold steak for sandwiches, and it should still be pink in the middle if you roasted it right. A 1kg joint is four people; the 2kg is six to eight; the 4–5kg is a do. Match the joint to the table. Gravy from the tin, horseradish, not a stew liquor — this is a dry roast, not a pot roast.
A 1kg sirloin joint is a small Sunday. The 2kg frozen joint is the one that actually looks like a roast on the board. The 4–5kg is a project: either a party roast or a morning of cutting steaks. Pick one job for that joint; it will not do both well in the same afternoon.
Probe 52–54°C, rest, carve thin. That is a sirloin joint, 1kg or 4kg, and it is the roast for people who already like sirloin steak.