*You can use either canned, jarred, homemade or the dry mix (made to directions)
Preheat oven to 400 degrees F. Lightly spray or grease 4 large ramekins (9-10 oz volume).
Unfold sheet of puff pastry and roll out to a 13-inch square. Cut the sheet into quarters. Lightly press 1 square of pastry into each ramekin, pressing up the sides. Let the corners hang over. Set aside.
Cut steak into cubes about 1/2-3/4-inch. If using leftover beef, cut it the same way.
Heat a large skillet over medium heat. Add butter to the pan and melt.
Add the beef and brown. Add the mushrooms, onions, thyme and pepper. Saute for about 5 minutes. Stir in gravy.
Divide steak/gravy mixture evenly between the 4 pastry-lined ramekins. Pull up the corners and pinch the points to almost seal. Brush the pastry corners with the beaten egg.
Bake for 20-25 minutes or until the pastry is a deep golden brown.