Preheat oven to 375F and move the rack to the top third of the oven.
Boil a salted pot of water for the pasta and cook it 2 minutes less than package directions suggest. Once the pasta is done, drain it and return it to the pot it was cooked in, then stir in the marinara sauce and about 1/3 of the package of pepperoni.
Transfer the mixture to a 9x13 baking/casserole dish and spread in an even layer.
Top with the mozzarella, then add the remaining pepperoni over top of the cheese.
Bake, uncovered, for 20 minutes, and then broil for a few minutes to crisp up the pepperoni and cheese (watch it carefully so it doesn't burn).
3 cups = a 24 ounce jar of marinara sauce. I prefer a little more sauce, so I usually open a second jar and add another 0.5-1 cup, but if you don't want to open another jar, stick with the 3 cups.
Sliced pepperoni comes in a variety of package sizes, so you may need to buy more than one for the 10 ounces. Anything that's a little less or little more will work fine.
See blog post for ideas for recipe variations.
Nutritional information is provided as a courtesy only and should be construed as an estimate rather than a guarantee. Ingredients can vary and Salt & Lavender makes no guarantees to the accuracy of this information.