Pressure cook the ox tongue in water mixed with sliced onions, bay leaf, salt, and white pepper (45 minutes for 1/4 kilo ox tongue). If pressure cooker is not available, boil tongue in 6 to 8 cups of water until tender, about 3 to 4 hours.

Peel-off the white outer covering of the tongue and slice diagonally about 1/2 inch thick. Set aside.

In a pan, heat 1/2 cup butter. Add the sliced onions and cook over low fire until transparent. Add tongue and sliced mushrooms; continue cooking for 5 minutes. Add the all-purpose flour. Mix together in a brisk motion, but don't mash the tongue. Slowly pour-in the broth, stirring all the time to prevent sauce from getting lumpy. Add milk and grated cheese. Check seasoning. Set aside.

To make the crust: In a mixing bowl, sift the flour. Cut-in the margarine until flour is pea sized. Toss in 1/2 cup water until the mixture sticks together. Form into a ball and roll out on a floured board to fit your pyrex dish. Brush with egg wash. Bake in 350 degrees Fahrenheit oven for 25 minutes. Brush again with egg wash and bake for another 15 minutes or until brown. Pour the tongue mixture onto the crust.