To make the pie dough, in a large bowl, whisk together the flour and salt. Add the butter and work it in with either your hands or a pastry blender until it resembles coarse crumbs. Stir in the shredded cheese and add the water. Use a rubber spatula to work the dough until it just comes together, adding more water a tablespoon at a time, if needed. Form the dough into a large disk and wrap tightly in plastic wrap. Chill for at least 30 minutes before using.

Make the bacon jam: heat a large pot over medium-high heat. Add the bacon and cook, stirring often, until the fat renders and the bacon is crispy, about 7 to 9 minutes. Using a slotted spoon, transfer the bacon to a plate lined with a paper towel.

Drain off all but 1 tablespoon of the bacon fat from the pot. Add the onion and cook until tender and translucent, about 7 to 9 minutes. Add the brown sugar and cook, stirring often, until fully dissolved. Stir in the apple cider and cider vinegar and bring the mixture to a simmer. Reduce the heat to low and simmer, uncovered, stirring often, until the liquid reduces almost entirely and the onions are very tender, about 8 to 10 minutes. Stir in the garlic.

Season the mixture with the chili flakes and lots of black pepper and stir until well combined. Return the bacon to the pot and stir. Use an immersion blender (or transfer to a food processor) and puree mixture until thicker and slightly smoother. Allow to cool completely.

Preheat oven to 425°F. Line two baking sheets with parchment paper and set aside.

On a lightly floured work surface, roll out the dough to a square slightly larger than 16 by 16 inches. Trim the edges with a pairing knife so they are straight. Cut the dough into 16 equal pieces. Transfer the squares to the prepared baking sheets, staggering them slightly (they can be close to each other).

Brush the squares with egg wash and prick all over with a fork. Press a 2 1/2-inch round cookie cutter gently into the center of each square, not pressing all the way down, to score the dough and give you a guide for filling. Scoop about a rounded tablespoon of the bacon jam mixture into the center of each square of dough. Transfer the pans to the oven and bake until the crust is deeply golden brown and the bacon jam has deepened in color, about 30 to 35 minutes. Cool for 15 minutes before serving.

In a large bowl, toss together the arugula, tomatoes, olive oil and a large pinch of salt and pepper until evenly combined. Top each cooled pie with this mixture and with the shaved parmesan if using. Enjoy!