Before starting, preheat the broiler to high. Wash and dry all produce. Add 10 cups water and 2 tsp salt to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat. Add penne to the boiling water. Cook uncovered, stirring occasionally, until tender, 10-12 min. Drain and return penne to the same pot, off heat.

While water comes to a boil, peel, then cut shallot into 1/4-inch pieces. Peel, then mince or grate garlic. Roughly chop spinach. Drain, then rinse olives. Pat dry with paper towels, then roughly chop. Pat bocconcini dry with paper towels. Tear bocconcini into quarters, then season with 1/4 tsp garlic salt (dbl for 4 ppl) and pepper.

Once penne is added to the boiling water, heat a large oven-proof pan over medium heat. When hot, add 1 tbsp oil (dbl for 4 ppl), then shallots and garlic. Cook, stirring constantly, until softened and fragrant, 2-3 min.

Add crushed tomatoes, olives, 1/2 tsp chili flakes and 1/4 cup water (dbl both for 4 ppl) to the pan with shallots. Cook, stirring occasionally, until sauce thickens slightly, 4-5 min. Remove from heat. Stir in 1 tbsp balsamic glaze (dbl for 4 ppl). Season with 1/4 tsp garlic salt (dbl for 4 ppl) and pepper.

Add sauce, spinach and half the bocconcini to the pot with penne, then stir to combine. Transfer penne to the same oven-proof pan. (NOTE: If you don't have an oven-proof pan, transfer penne to an 8x8-inch baking dish for 2 ppl; 9x13-inch for 4 ppl.) Arrange remaining bocconcini over penne. Sprinkle Parmesan over top. Broil in the middle of the oven until cheese melts, 4-5 min.

Divide penne al forno between plates. Sprinkle remaining chili flakes over top, if desired. Drizzle with remaining balsamic glaze, if desired.