Heat the olive oil and butter in a large pot over medium heat. Add the shallot and saute until translucent, about 3 minutes. Add the garlic and cook until fragrant. Stir in the pumpkin, cream, chicken broth and crushed red pepper flakes, and a pinch each of salt and pepper. Simmer for 10 minutes or until the sauce thickens slightly. Taste and adjust seasonings as needed.
Meanwhile, in a large pot of salted boiling water, cook rigatoni according to package direction for al dente. Using a large slotted spoon, transfer pasta from pot to sauce; stirring to coat in the sauce.
On a large serving dish, plate pasta with some fresh basil and serve.
