Cut the oxtail in half to make it easier to work with. You can use any heavy sharp knife; a regular chef’s knife or cook’s knife will do.
Grasp a piece of the oxtail by one of the ends; it doesn’t matter which end. Use a towel to improve your grip if you need to.
Position the blade of a chef’s knife or filet knife facing away from you against the fat covering the tail at a slight downward angle.
Slice the fat off the tail in strips. Slice a strip of fat off, rotate the tail in your hand a little, then slice another strip of fat off.
Turn the tail around and grasp it by the other end and repeat. Strip the fat off the other half of the tail when you finish with the first.
Go over the tail halves again with the knife, slicing away any pieces of fat that you missed the first time around. Trim off the loose pieces of fat and connective tissue that hang off the wide end of the tail, the end that was connected to the rump of the animal.
Slice the tail into segments using the space between the bones as a guide. The spaces between the bones become visible when you trim the fat away. The tail bones are connected to each other with tissue similar to ligaments, and you can use a chef’s knife or cook’s knife to sever them.