For the bolognese: Heat the oil in large saucepan over medium heat. Add the garlic and chili flakes, and fry until golden, about 1 minute. Add the onions and saute until the edges are crispy, 8 to 10 minutes. Throw in the sirloin and saute for 5 minutes until the beef is crumbled. Add the San Marzano tomatoes, fresh parsley, oregano, raw sugar, bay leaf, sea salt and some pepper. Stir and simmer for 20 minutes.
For the pasta: Bring salted water to a boil. Throw in the pasta and cook until almost al dente, 8 to 9 minutes. Drain. To assemble: Preheat the oven to 350 degrees F. Grease a 15-by-10-inch baking dish, 2-to-3-inches deep, with the butter.
In a bowl, mix the pasta with half the bolognese sauce. Lay down a thin layer of pasta, 1/4 cup sauce, 1/3 cup mozzarella and 1 tablespoon Parmigianno. Repeat until all the pasta is used. Top off with mozzarella. Place in the oven and bake until the edges are golden and bubbling, about 30 minutes.