In a one cup measuring cup, break the egg for the pie crust, and beat the egg until it is a light lemon yellow. Add one tablespoon of vinegar, stir, and then fill rest of the cup with water, and set aside.
In a large bowl, add the 2 ½ cups of flour, salt, and shortening.
Cut the shortening into the flour with a pastry blender until it resembles small pea size particles.
Add the egg/water mixture, and blend into the flour mixture, until all the liquid is absorbed.
With your hands, form the dough into a ball, and place on parchment paper.
Roll dough out to fit a 12 inch iron skillet, and place the dough in the skillet bottom and up the sides, and pinch the top forming a decorative edge. Set aside.
In a food processor, add the eight eggs, cream, and Parmesan cheese, and blend the mixture until it is a light lemon color.
Add the spinach, Feta cheese, salt, pepper, Italian seasoning, flour, and baking powder, and mix.
Remove the bowl from the food processor, and gently fold in the tomatoes.
Pour the egg filling into the crust, and top with a little more Parmesan cheese.
Place the Cast Iron skillet in the oven at 350 degrees for 45 minutes to 1 hour, or until the Quiche is golden brown, and a knife inserted in the center comes out clean. Allow it to set up for 10-20 minutes before cutting.
Reheating: To reheat quiche, preheat oven to 350 degrees. Heat up for 15 minutes or until center is warm. To Freeze Leftovers: Freeze leftover slices of quiche by wrapping each slice up in foil or Press n Seal. I like to then place the slices in a freezer safe Ziploc bag and label. When you are ready to eat, remove from the freezer and microwave for 2- 2 ½ minutes.Substitute Dough: Substitute refrigerated dough for the homemade dough. Substitute Tomatoes: If substituting tomatoes, make sure to remove as much moisture as possible. Crustless Option: Make this without a crust by simply spraying the bottom of a pie pan with non stick spray and pouring the egg mixture inside. The pie pan capacity likely will be less than a cast iron skillet so just be prepared for having a little extra. If that happens, pour the leftover quiche egg mixture into muffin cups and cook for 15-20 minutes or until the muffin sized quiche is done. To Make Quiche Cups: You can make these crustless Spinach Tomato Quiche Cups using a muffin tin. Prepare the egg mixture in the recipe box and then divide and pour into 12 muffin cups that are sprayed with non stick spray. Cook at 350 degrees for 15 minutes or until done in the center that is tested with a toothpick. These can be re-heated in the microwave for 90 seconds. Make Ahead: Prepare all the way until right before you put in the oven. Cover and put in the refrigerator. The next day, remove from the refrigerator for 30 minutes before you are ready to cook. This allows the food to come back down to room temperature and will evenly cook. If you don't do this, it will need longer to cook and you should reduce your oven temperature. I am recommending to leave it out for 30 minutes FIRST and then proceed as the directions state.