The general rule for roasting beef sirloin is to calculate the time based on its weight and your desired doneness. For a standard oven at 180°C (Fan), cook for 15 minutes per 500g plus 15 minutes for rare, 20 minutes per 500g plus 20 minutes for medium-rare, 25 minutes per 500g plus 25 minutes for medium, and 30 minutes per 500g plus 30 minutes for well-done.

The ideal internal temperature for a perfect medium-rare sirloin roast is 55-57°C (131-135°F). At this temperature, the centre will be warm and red, juicy, and tender. Always remove the roast from the oven when the meat thermometer reads about 2-3 degrees lower than your target, as the temperature will continue to rise while the meat rests.

It is generally recommended to roast a sirloin uncovered to allow the outside to brown and develop a delicious crust. However, if the roast is browning too quickly before the inside is cooked, you can loosely tent it with foil for the remainder of the cooking time. Always cover it with foil during the resting period to keep it warm.

Resting the meat is absolutely crucial. When meat cooks, the muscle fibres contract and push the juices to the centre. If you carve it immediately, those juices will spill out onto the board, leaving you with dry meat. Resting for 15 to 30 minutes allows the fibres to relax and the juices to redistribute throughout the roast, resulting in a much juicier and more flavourful carve.

Searing the sirloin before roasting is optional but highly recommended for extra flavour. Searing in a very hot pan with a little oil creates a Maillard reaction, forming a rich, brown crust that enhances the overall taste of the roast. If you sear it first, you may need to reduce the oven cooking time by 5 to 10 minutes.

While a meat thermometer is the only truly accurate method, you can use the ‘finger test’ to estimate doneness. Press the centre of the roast: if it feels very soft and squishy, it is rare; if it yields slightly and feels springy, it is medium-rare to medium; if it feels firm and springs back quickly, it is well-done. However, this method takes practice and is less reliable than a thermometer.

It is strongly advised not to cook a sirloin roast from frozen. Cooking from frozen will result in an overcooked exterior and a raw, cold interior, and it poses food safety risks. Always thaw your roast completely in the refrigerator for 24 to 48 hours before cooking to ensure even cooking and food safety.

A sirloin roast is cut from the upper rear part of the cow and is generally very tender, well-marbled, and flavourful, making it ideal for roasting whole. A sirloin tip roast comes from the round (the rear leg), which is a heavily exercised muscle. It is much leaner and less tender, requiring slower, moist cooking methods or very careful roasting to prevent it from drying out.