Add water to a large stockpot and salt liberally and bring to a boil. Cook your pasta according to the directions (al dente). While we cook the pasta, let's make the sauce.
In a large sauté pan, melt 8 tbsp unsalted butter over medium heat until just foaming. Then, add in 1/2 cup heavy whipping cream, while whisking, until combined.
Next, add 1/4 cup sun-dried tomato pesto, lemon zest and juice, salt, pepper, and red pepper flakes. Mix until combined. Turn the heat down to medium-low. Let the sauce simmer for about 5 minutes, stirring and scraping up any browned bits on the bottom.
When the pasta is finished cooking, strain and add it to the pesto cream sauce. Remove the sauté pan off the heat, add 1/2 cup basil leaves, and use tongs to toss. Continue to toss until the pasta is evenly coated in the sauce. Serve immediately.
Notes
Reserve pasta water: A splash of starchy pasta water helps loosen the pesto rosso and creates a silky sauce that coats the pasta evenly.
Pasta shape matters: Short, ridged shapes or twists hold pesto rosso best, but long noodles work beautifully too if tossed thoroughly.
Finish gently: Warm the pesto rosso with the pasta just until coated. Avoid high heat so the sauce stays rich and vibrant, not oily.