Bring a large pot of salted water to a boil and cook the penne pasta according to package instructions until al dente.
While the pasta is cooking, heat a large skillet over medium heat.
Add a drizzle of olive oil to the skillet and heat until shimmering.
Add the diced onion to the skillet and cook until softened and lightly browned, about 5-7 minutes.
Add the minced garlic and crushed red pepper flakes (if using) to the skillet and cook until fragrant, about 1 minute.
Add the tomato paste to the skillet and cook for 2-3 minutes until it has darkened in color.
Add the vodka to the skillet and cook for 2-3 minutes until it has reduced by half.
Add the crushed tomatoes to the skillet and bring the sauce to a simmer.
Stir in the heavy cream and cook until the sauce has thickened slightly, about 5-7 minutes.
Season the sauce with salt and pepper to taste.
Reserve some of the pasta cooking water and drain the penne pasta.
Add the cooked penne to the skillet with the sauce and toss to combine.
If the sauce seems too thick, add a few tablespoons of the reserved pasta cooking water to the skillet to loosen it up.
Serve the penne with vodka sauce hot, garnished with fresh chopped basil, if desired.