Preheat oven to 450° F (230° C).
In a very large bowl, mix meat with potatoes, onion, lard (if used), and generous grindings of Sea Salt and Pepper.
Cover the bottom and sides of roasting pan (no rack) with pastry. Add meat and potato mixture and pour Bouillons overtop. Add water, if needed, so meat and potatoes are covered with liquid. Arrange bay leaves overtop.
Cover with pastry and seal sides to prevent leaking. Lightly beat egg yolks with water. Brush over top of pastry. Using a knife, slash pastry in 2 or 3 places. Cover with foil.
Bake for 1 hour, then reduce heat to 325° F (160° C). Continue to bake for 5 hours. Occasionally check that the foil is not sticking to pastry.
After 5 hours, reduce heat to 300° F (150° C). Remove foil and continue to bake for 1 more hour. Remove from oven and let stand 10 minutes before cutting.
In a very large bowl, blend 14 cups (3.3 L) flour with 2 tsp salt.
Using a pastry blender or 2 knives, cut in 2 lb (0.9 kg) trans fat-free chilled shortening (cut into cubes first) until mixture resembles coarse crumbs. Add 3 cups cold water.
Using a large fork or your hands, gently stir to combine.
Add up to 1⁄4 cup cold milk if dough is too dry to hold together.
Shape dough into 2 balls, then flatten into discs.
Wrap each in plastic and refrigerate for 30 minutes, or up to 2 days before rolling out.