In a large bowl, stir together the flour, sugar, and salt until combined. Using a pastry cutter or clean hands, cut the butter into the flour mixture until it's worked in, and the mixture has small chunks of butter running throughout. In a small bowl, stir together the egg, cold water, and vanilla extract until combined. Pour the wet mixture into the flour mixture, and use a fork to stir it together until a dough forms. Once you have a shaggy dough, turn it out onto your work surface. Gently knead the dough until it comes together in a large mass. It will still be a big shaggy.

Lightly flour your work surface, and roll the dough out into a long rectangle, about 15-18 inches long. Fold the dough into thirds, turn 90 degrees, and repeat the process two more times. By the time you reach the third fold, your dough should be much more cohesive. Wrap the dough tightly in plastic wrap, and chill for at least 30 minutes before rolling it out to bake.

Heat a large skillet over medium heat. Slice your onion into half-moon slivers or into a small dice, whichever you prefer. Melt your butter in the pan, and add in the onions. Stirring frequently, cook the onions for about 3 minutes, or until they start to become translucent. Reduce the heat to low, and add in the salt and pepper. Let the onions cook on low heat, stirring occasionally, until they become a deep golden caramel color. For me this takes about 20 minutes.

While they cook, if the pan becomes dry, add in a splash of water as needed to keep the onions hydrated as they caramelize- this helps them cook more evenly. Once the onions are almost done, with just a few minutes left of cook time, add in the worcestershire sauce and minced garlic and cook for another 1-2 minutes. Set the onion mixture aside to cool completely. Once cooled, stir the onions with your softened cream cheese until well combined.

Preheat your oven to 375 degrees, and line a large baking sheet with parchment paper. On a lightly floured surface, roll out the pie crust until it's about 1/4 inch thick. Optionally, trim the edges to make a less-shaggy circle. Transfer the dough to the prepared baking sheet. Spread the cream cheese mixture on the crust in the middle, leaving about 1 inch of space all around it. Pile the sliced tomatoes on top. Then, fold the edges of the dough up around the filling- this doesn't have to look perfect!

Beat the egg in a small bowl, and brush the egg all over the edges of the crust generously. Optionally, sprinkle a little more salt and black pepper on the edges and top of the pie. Bake for 35-40 minutes, or until the crust is a deep golden brown. Cool for 15 minutes, and slice to serve!