only ever made it once with cabbage and am not a fan, but when did the beef was blushed with mustard, topped wothe duxelle then wrapped in the blanched cabbage and left overnight before folded in pastry, it worked out fine. as I say not my prefered method but have experienced it
Knew a french chef used to do beef en croute in a similar way but would wrap the fillet in savoury crepes before the pastry as a barrier.
Don't think there is an exact way if honest, as long as it's beef, duxelle and pastry it can be modified as required