Bring a large pot of salted water to a rolling boil. Add the short pasta and cook until very al dente — 2 minutes less than package directions (about 8–9 minutes depending on pasta). Reserve 1 cup of pasta cooking water, then drain the pasta and set aside.

Preheat the oven to 375°F (190°C). Lightly oil a 9x13-inch baking dish or a similar casserole.

Make Ricotta Filling

In a medium bowl, combine the ricotta, grated Parmigiano-Reggiano, egg, lemon zest, chopped basil, and minced garlic. Stir until smooth and homogenous.

Season the ricotta mixture with salt and freshly ground black pepper. Drizzle in 1 tablespoon extra-virgin olive oil and mix to incorporate. Taste and adjust seasoning — if the ricotta tastes flat, add up to another 1/4 teaspoon salt or a pinch more lemon zest.

If using optional spinach, fold the blanched, squeezed-dry chopped spinach into the ricotta now; if using crushed red pepper flakes or pine nuts, reserve for assembly or topping as desired.

Combine and Assemble

In a large bowl, combine the cooked pasta with 1 to 1 1/4 cups of the tomato sauce. Add 1/4 cup of the reserved pasta water if the mixture seems stiff; the goal is a saucy but not soupy pasta that will bake well.

Transfer half of the sauced pasta into the prepared baking dish and spread into an even layer.

Spoon dollops of the ricotta filling across the first pasta layer, spacing them evenly (about 8–10 dollops). Use the back of a spoon to gently spread the ricotta into a thin, even layer but leaving some pasta visible — this helps pockets of cheese remain in the bake.

Scatter half of the shredded mozzarella and a tablespoon of grated Parmigiano-Reggiano over the ricotta layer.

Top with the remaining pasta and remaining tomato sauce. If the bake looks dry, loosen with up to 1/4 cup reserved pasta water. Finish by sprinkling remaining mozzarella and the remaining 2 tablespoons grated Parmigiano-Reggiano evenly over the top. If using red pepper flakes or toasted pine nuts, sprinkle them now.

Bake and Finish

Cover the dish with foil (tenting slightly so the cheese doesn't stick) and bake in the preheated 375°F (190°C) oven for 15 minutes.

Remove the foil and bake uncovered for another 10–12 minutes, or until the top is bubbly and golden and the cheese is melted through.

If you prefer a more-browned top, place under a hot broiler for 1–2 minutes — watch closely to avoid burning.

Remove from the oven and let rest for 5–8 minutes. Garnish with fresh basil leaves torn or chiffonade. Drizzle a little extra-virgin olive oil over the top if desired, and serve hot, passing additional grated Parmigiano-Reggiano at the table.