Heat a saucepan over medium heat. Add the oil and butter and cook until foaming. Add the onions and saute until translucent, about 10 minutes. Add the tomato paste and cook for another minute. Add the crushed red pepper, garlic and some salt and pepper. Cook for 30 more seconds. Add the vodka off heat and deglaze the pan. Add the crushed tomatoes and simmer until the alcohol smell subsides, about 8 minutes. Add the cream and season to taste.
Meanwhile, bring a pot of water to a boil and salt generously. Cook the pasta to al dente, 4 to 5 minutes for fresh, or according to the package instructions.
Toss the sauce with the hot pasta and garnish with fresh basil and grated Parm. Serve with a crusty hunk of Italian bread.
Combine the 00 and semolina flours with the salt on a clean working surface, form into a mound and make a well in the center. Add the water and olive oil (see Cook's Note). Using a fork, start to mix the dry ingredients into the wet until a shaggy mass forms. Knead vigorously until the dough is smooth, elastic and bounces back when pressed, about 10 minutes.
Cut the dough in half and work with one piece at a time (cover the other piece with a clean, damp kitchen towel). Using a bench scraper or knife, cut a walnut-sized piece of dough and roll it into a thin rope about 1/3 inch in diameter. Using the 4 fingers of your hand (no thumb), roll the rope of dough back and forth until it is a long, slender, tube-like shape (but not enclosed like a tube). Set aside on a clean town sprinkled with semolina flour. Repeat with the remaining dough.
To cook, generously salt a large pot of boiling water. Add the cavatelli and cook until al dente, 4 to 5 minutes. Drain and use with your sauce recipe of choice.
If it is a damp or rainy day, add three-quarters of the water and oil mixture, then add the rest a little bit at a time until the dough comes together. The dough can absorb moisture from the air.