In a large saucepan, saute 2 cups chopped onion and 2 garlic cloves, crushed, in 14 cup butter or margarine until onion is transparent.
Next, moisten with water both sides of 1 (2-lb.) piece stewing beef and sprinkle each side with half of 1 teaspoon instant meat tenderizer.
Pierce meat all over with a sharp-tined fork and cut into 1-inch cubes.
Add to saucepan containing onion and garlic, with 1 cup water, 1 bay leaf, 1 whole clove and 10 peppercorns.
Bring to boil, reduce heat.
Simmer, covered, 15 minutes.
Meanwhile cut 1 lb. beef kidneys in half and remove all tubes and gristle.
Cut into 1-inch dice and place in a small saucepan along with 1 cup water and 1 teaspoon salt.
Bring to a boil and cook, uncovered, 5 minutes.
Drain well and add to simmering beef mixture.
Simmer 45 minutes more.
Stir in 1 (10 1/2-oz.) can beef gravy, 1/2 lb. fresh mushrooms, quartered (or 2 [4-oz.] cans, sliced mushrooms drained), 12 fresh oysters, shucked (or 1 [4-oz.] can oysters) and 1/2 cup oyster liquor.
Simmer 10 minutes, then pour into a large, shallow casserole and set aside.Gently press together 6 individual shells from 1 (10-oz.) pkg.
frozen puff pastry shells, thawed.
Roll out to make a sheet of pastry 1 inch larger than top of casserole dish containing meat mixture.
Trim off a 1/2-inch strip of dough all around.
Moisten edge of casserole with water and press the 1/2-inch strip of dough onto edge of dish.
Moisten this dough with water.
Fit top crust on over beef and kidney mixture and seal edges together.
Cut fancy shapes from any dough trimmings.
Moisten back of shapes with water and place on crust.
Cut 2 or 3 slits in top of pastry to allow steam to escape and brush all over with a mixture of 1 egg yolk beaten with 1 tablespoon milk.
Bake 20 minutes at 450°, or until crust is rich golden brown.