Make the pesto by blending the fresh basil, pine nuts, grated Parmesan, and garlic in a food processor. As it runs, slowly drizzle in olive oil until you get a smooth consistency. Season with salt and pepper to taste, then set the pesto aside.
Cook your pasta in salted water until al dente, following the package instructions. Drain the pasta and set it aside for later. Reserve ½ cup of pasta water.
In a large skillet, heat some olive oil over medium heat. Add the chopped onion and sauté for about 3-4 minutes until softened. Add the minced garlic and cook for another minute until fragrant.
Next, add the ground beef and cook it until browned, breaking it apart as it cooks, about 5-7 minutes.
Once browned, stir in the tomato paste and red pepper flakes. Let the mixture cook for another 2 minutes to blend the flavors.
Pour in the heavy cream and let it simmer for a few minutes to thicken slightly. Once the sauce has thickened, stir in the fresh pesto and mix everything well. Add some of the reserved pasta water if the sauce is too thick.
Toss the cooked pasta into the skillet, ensuring it's fully coated with the creamy, spicy pesto beef sauce.
Serve hot with extra Parmesan cheese.