Lightly grease your springform pan with butter. On a well-floured surface, roll out the full batch of pie dough out to a 17-inch round (leave the half batch in the refrigerator). Fold the edges of your dough in so you have a square smaller than your springform pan that you can pick up. Place the dough inside the pan and unfold it, gently manipulating the dough so it is evenly distributed over the pan. Trim the overhang so only 1 inch remains.
If there are any tears, patch them with the scraps, using a tiny bit of water as glue. Place the pie crust in the refrigerator.
In a large pot (with a lid), cook bacon over medium heat until cooked through but not too crispy. Use a large slotted spoon to transfer bacon to a plate, leaving the bacon drippings.
Add ground pork to the pot. Sprinkle with salt and pepper, and cook over medium until cooked through. Use your large slotted spoon to remove pork and transfer to a second plate. Add onions to the the pot and cook over medium for 4 to 5 minutes until onions are just starting to turn translucent around the edges. Add in the rest of the diced vegetables and the cooked ground pork.
Add 1 cup water and cover. Simmer covered for 10 minutes. Uncover, stir, and continue to simmer uncovered until water is evaporated and vegetables are just fork tender.
Make the Gravy
While your meat and vegetables simmer, in a medium saucepan, melt butter over medium heat. Whisk in flour and cook until lightly browned, about 1 minute. Whisk in broth, beating out any lumps that form. Continue to cook, whisking constantly until mixture thickens and begins to bubble, 4 to 6 minutes. Remove from heat and set aside.
Once your meat and vegetables are done, stir in the gravy. Add rosemary, oregano, and salt and pepper to taste. Your mixture should be fairly salty. Don't be afraid to add more!
Cool for at least 30 minutes, stirring occasionally to speed up the cooling process. Once mixture is mostly cooled, stir in bacon.
Make sure your pie dish will fit in your oven, if not, move the top rack down. Preheat your oven to 400°F and place a rimmed baking sheet on the top rack to catch drips in case your pan leaks and to help cook your bottom crust (if using a glass or ceramic pie pan, skip this step as a hot baking sheet can cause them to shatter).
In a small bowl, whisk the egg white until frothy and brush over the inside bottom of your chilled, prepared pie crust. Pour meat mixture over the top, mounding it the highest in the center, and roll out your half batch of dough for the top. Place dough over the top of your pie and trim the overhang so that it is even with the bottom crust. Roll the dough under and either flute or crimp the edges to seal. Just make sure all of the crust is inside of the springform pan so it doesn't break when you release the pan.
Whisk together egg and milk and brush over the top of the pie.
Cut a few slashes in the top of the pie for steam to escape.
Place your pie on the preheated tray in the oven and bake for 55 to 65 minutes, until the crust is cooked through and filling bubbly. Check on the pie at around 40 minutes and cover loosely with foil if browning too quickly.
Allow pie to cool in the pan (do not open up the springform pan) for at least 15 minutes before releasing and cutting.