(You'll need to prepare the calzone dough ahead of time. This will take about 45 minutes from start to finish. Or you can prep it up to 3 days in advance, wrap in plastic wrap, and store in the fridge until ready to use it.)
Prep: Preheat oven to 400°F degrees. Adjust oven racks to be equidistant from the middle. Line two sheet pans with parchment paper (or foil).
Make Filling: In a medium bowl, combine ricotta, Parmesan, mozzarella, pepperoni, 2 eggs, parsley, Italian seasoning, salt, pepper. Set aside.
Roll Out Dough: Dust flour on a clean surface to work with the dough on. Divide the dough ball into 8 equal pieces. Working with one piece at a time, roll it into a ball and then roll it out into a very thin circle, about 1/4 inch thick.
Fill & Seal Calzones: Spoon 3-4 tablespoons (approximately) filling onto half of each dough circle, leaving a little room around the edges. (Do not overfill the calzone or it will split open while baking.) Fold half of the dough over itself to close it, then press edges to seal. Use the back of a fork or roll and pinch the edges to make sure it's sealed well. Poke a few holes with a fork in the top of each calzone. Transfer them to the two lined baking sheets.
Egg Wash: In a small bowl, whisk together the remaining egg and a splash of water. Brush the surface of each calzone with the egg wash using a pastry brush (or your fingers if you don't have one!). Optional: Sprinkle a little grated Parmesan and Italian seasoning over the top of each one. Bake: Place the pans in the oven and bake for 10-15 minutes, until nice and golden brown, rotating the pans halfway through the bake time. Let cool for about 10 minutes and serve with ramekins of warm marinara sauce for dipping.