Soak sweetbreads in cold water for 1 hour. Rinse and place in pot. Cover with additional cold water. Bring slowly to a boil, then drain immediately and plunge into a bowl of cold water. Remove skin and press sweetbreads between 2 plates. Wrap plates in a towel, place a heavy weight on top, and compress for 30 minutes. Blot sweetbreads dry after pressed.
For pastry: Make well in center of flour. Add salt and butter. Combine quickly with water to form a smooth dough. Knead lightly and let rest for 30 minutes in a cool place. Remove and roll out to a size slightly larger than the lip of a pie pan.
To assemble: Preheat oven to 375 degrees F. Heat clarified butter in pan. When hot, add bacon and fry. Line pie dish with half the bacon, cover with a layer of sweetbreads. Add remaining bacon and remaining sweetbreads. Moisten with lemon juice and cover with tomatoes. Season with pepper and marjoram leaves.
Lightly brush lip of pie pan with water. Cover filling with pastry and press down at edges to seal. Trim off excess dough. Cut vent holes in center and brush dough with egg. Bake 45 minutes.