Beef Carpaccio with Mustard Dressing

Chill 4-6 serving plates in the refrigerator.  Meanwhile, prepare the beef; loosely wrap the fillet in foil or baking parchment and place in the freezer for 10-15 minutes. 
To make the mustard dressing, place all the ingredients into a screw-topped jar and shake well.   
Remove the beef from the freezer and slice as thinly as possible across the grain of the meat. 
Place each slice between two sheets of cling film and using a rolling pin or meat mallet flatten evenly into wafer-thin slices. 
Stack the slices, still covered in cling film and chill until required.