Cook the Pasta: Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions, until al dente 1 (cooked through but still slightly firm to the bite). Reserve 1 cup of pasta water before draining.
Sauté the Aromatics: While the pasta cooks, heat oil in a large skillet over medium heat. Add the chopped onion and cook for 3-4 minutes, or until softened and translucent. Stir in the minced garlic and cook for an additional minute, until fragrant. Be careful not to burn the garlic.
Build the Sauce: Add the tomato paste to the pan and cook for 2-3 minutes, stirring constantly. This allows the tomato paste to deepen in color and release its full flavor.
Creamy Dream: Pour in the heavy cream and red pepper flakes (adjust the amount for your spice preference). Season with salt and pepper to taste. Let the sauce simmer for 1-2 minutes, allowing the flavors to meld.
Pasta Party: Drain the cooked pasta and add it directly to the pan with the sauce. Toss to combine.
The Perfect Finish: Add the reserved pasta water, one tablespoon at a time, until the desired consistency is reached. You want the sauce to be creamy and coat the pasta evenly, but not too thin. Stir in the butter and grated cheddar cheese. Toss everything together until well combined.
Serve and Enjoy: Plate the pasta and garnish with fresh chopped basil leaves. Add some grated cheese on top for garnish as well. Serve immediately and enjoy!