Cook first 5 ingredients in frying pan until all liquid is absorbed and mixture resembles a paste.
Partially thaw pastry shells and roll out thin enough to cover top, sides, and part of the bottom of each steak.
Cover with plastic wrap and store in refrigerator until serving time.
Cook steaks on rack, uncovered, for 25 minutes.
They will be rare but will continue cooking while dish is readied.
Serve with Bearnaise sauce.