1Pour milk and heavy cream into a saucepan. Add 15g of salt. Heat gently over medium-low heat, stirring frequently, until it reaches 190°F/88C (about 5-8 minutes).
2Remove from heat and swirl in vinegar. Carefully and gently stir it in then let sit for 15 minutes until curds form.
3Line a strainer with cheesecloth and gently scoop the curds into the cloth. Let the cheese drain for 20-30 minutes.
4Bring a pot of salted water to a boil. Add the jumbo shells and cook for about 6 minutes, until almost al dente.
5Drain and toss gently with olive oil to prevent sticking. Set aside.
6Stack prosciutto, slice it into strips, then finely mince into small pieces.
7Heat a Dutch oven over medium heat with a drizzle of olive oil. Add the minced prosciutto and fry for 90 seconds, being careful not to crisp it.
8Add 15g/3 cloves minced garlic and cook for another minute. Stir in spinach and cook until wilted, about 2 minutes.
9Transfer to a cutting board, chop finely, and squeeze out any excess moisture with a towel.
10Wipe out the Dutch oven. Add a drizzle of olive oil, then grated onion and 15g/3 cloves of minced garlic.
11Add a pinch of salt and sweat the mixture for 5 minutes.
12Stir in chopped Calabrian chiles (or chili flakes) and fry for 2-3 minutes.
13Add tomato paste and cook for 1 minute until it deepens in color.
14Pour in the can of crushed tomatoes, 7g salt, sugar, and a splash of water.
15Simmer for 5 minutes, then stir in chiffonade basil.
16Taste and adjust seasoning.
17In a medium bowl, combine the drained homemade ricotta, the prosciutto-spinach mixture, heavy cream, shredded mozzarella, 75g of grated parmesan, about 20 cranks of black pepper, and 1 large egg.
18Stir until well combined.
19Preheat the oven to 425°F/220C.
20Fill each shell with about 2-3 tablespoons of the ricotta mixture, tucking the cheese inside using your fingers or a spoon.
21Nestle the stuffed shells in the sauce (I just do this in my dutch oven, but you can transfer to a baking dish if needed), arranging 18-22 shells in a crown pattern, making sure they are at least halfway submerged.
22Sprinkle a generous amount of grated parmesan over the shells.
23Cover the dish with a lid and bake for 15 minutes.
24Remove the lid and bake uncovered for another 15 minutes to allow the cheese to brown and the sauce to thicken slightly.
25Top with additional grated parmesan.
26Scoop out 3-4 shells per serving, top with more grated parmesan, and drizzle with a bit of spicy finishing olive oil.