1. Preheat your oven to 375°F (190°C). Lightly coat a 9×13-inch baking dish with cooking spray or a thin drizzle of olive oil.

2. Bring a large pot of water to a rolling boil. Season generously with kosher salt. Add the jumbo shells and cook until just al dente (about 2 minutes less than package directions). Drain shells and immediately toss with 1 tsp olive oil to prevent sticking.

3. While the pasta cooks, heat 1 Tbsp olive oil in a medium skillet over medium heat. Add the chopped onion and cook, stirring occasionally, until softened and translucent, about 5 minutes.

4. Stir in the minced garlic and red pepper flakes (if using); cook until fragrant, about 30 seconds.

5. Pour in the crushed tomatoes. Add oregano, a pinch of sugar (if desired), and season with salt and pepper. Bring to a gentle simmer, lower heat, and cook until slightly thickened, about 10 minutes. Remove from heat.

6. In a medium bowl, combine ricotta, beaten egg, Parmesan, 1 cup mozzarella, chopped parsley, and a generous crack of black pepper. Taste and adjust seasoning.

7. Spread about 1 cup of the tomato sauce in the bottom of the prepared baking dish, just enough to coat.

8. Stuff each shell with about 2 Tbsp of the cheese mixture and arrange them seam-side up in a single layer in the dish.

9. Spoon the remaining sauce evenly over the shells. Sprinkle the top with the remaining ½ cup mozzarella and additional Parmesan, if you like extra cheesiness.

10. Cover the dish tightly with foil and bake until heated through and bubbly, about 25 minutes.

11. Remove foil and bake until the cheese on top is melted and just starting to brown, 8–10 more minutes.

12. Let rest for 5 minutes. Garnish with extra chopped parsley before serving.