There are two main steps in preparing a roasting joint so that it's juicy and evenly cooked: trimming the fat and tying it up.
Trim the fat
Not every roasting joint needs to be trimmed; some are quite lean already. But trimming any excess fat from the outside of a joint can help cut calories. You always want to leave a little fat for moistness and flavour, but a big slab of fat can be trimmed away easily without ruining your joint.
To trim the fat, use a chef's knife with a smooth, sharp edge. Don't use a serrated knife because you'll end up with jagged cuts and damage the meat.
To make fat removal easier, chill the joint so the fat is solid. This helps the fat separate cleanly from the meat.
Lift up an edge of the fat. Hold the knife parallel to the surface of the meat and carefully make smooth, short cuts where the fat joins the meat. Keep lifting up the fat as you cut. The weight of the joint will help separate the fat from the meat.
If you look at the interior of a roasting joint, you'll notice veins of fat called marbling. This small amount of fat melts into the meat as it cooks. But if there's a big strip of fat running through the centre, you can cut open the joint and slice away the excess.
Tie it up
You tie a roasting joint to hold the meat together after it's been boned or butterflied. You can also tie up a joint if it is unevenly shaped. Tying the joint together helps the meat cook evenly.
Start by cutting a long length of kitchen string. It's going to wrap around the joint several times, so cut more than you think you'll need.
If your joint has been butterflied, roll it into a neat shape. Lay the joint on a cutting board with one end towards you.
Hold one end of the string and slip the string under the closer end of the joint. Bring the string together and tie a knot, leaving a short end of about 10cm, or 4 inches. Pull the string firmly to bring the meat together.
Now you're going to work with the long end of the string. Extend the long end of the string to about 4cm, or 1 1/2 in, further along the joint, and hold it there with your left hand.
Use your right hand to wrap the string around the joint. Loop the string through the piece you're holding down. Pull firmly to bring the meat together.
Continue extending, wrapping and looping all the way up the joint every 4cm.
To finish, turn the joint over, pulling the long end of the string over the end of the joint. You'll see a series of crossways pieces of string. You’re going to neatly connect all of them.
Loop the long end of the string around the first crossways piece. No need to wrap around the joint again. Just continue to loop the twine around the crossways pieces until you reach the end of the joint.
Now just flip it over one last time. You'll see where you started tying the joint. Just tie the short and long ends of the twine together to finish the job. Trim away the excess string.
Now you’re ready to proceed with your recipe! After your joint cooks, let it rest with the string still attached, then cut it off before slicing.