In a large skillet, cook the pancetta over medium-high heat until the fat is rendered and just beginning to brown, about 4 minutes. Add the onions and crushed red pepper; saute until soft and slightly caramelized, about 6 minutes.
Add the vodka and cook until reduced, 2 to 3 minutes. Add the tomatoes and stir well to combine. Cook for 15 minutes, then add the cream, and continue cooking until thickened, about 2 minutes. Remove from the heat and stir in the cheese.
In the meantime, cook the pasta in a large pot of salted, boiling water until just al dente. Drain in a colander, reserving 1 cup of pasta water for sauce. Toss the hot pasta in the skillet with the sauce to combine. Cook for about 2 minutes, adding reserved pasta water to loosen sauce, if desired.