Fillet of beef. To picture where the fillet comes from, think of chops all lined up, with the purely meaty bit in the middle all joined together. That is the fillet. Because fillet is such a sought after cut, they are not so often hung on the carcass nowadays, but are cut early from under the sirloin and vacuum packed. This is to preven them from losing weight so that the maximum price can be charged. However, this means that they leak blood so that often, when you cut open the packaging you find it awash. This means that the meat will be dry and flavourless. Fillet from a well aged, well hung animal is what you are looking for.