In a large pot of boiling salted water, cook the pappardelle pasta according to package instructions until al dente. Drain and reserve 1 cup of pasta water.
In a large skillet over medium heat, add the olive oil. Once hot, add the chopped onion and sauté for about 5 minutes until translucent.
Stir in the minced garlic and red pepper flakes, cooking for an additional 1-2 minutes until fragrant.
Pour in the heavy cream, stirring to combine. Then, add the halved cherry tomatoes. Let the mixture simmer for about 5 minutes, allowing it to thicken slightly.
Stir in the cooked pappardelle and season with salt and pepper. Add the grated Pecorino Romano cheese and mix thoroughly. If the sauce is too thick, gradually add reserved pasta water until the desired creaminess is reached.
Stir in the lemon zest for brightness and check for seasoning, adjusting with salt and pepper if needed.
Plate the pappardelle in bowls, garnishing with fresh basil leaves and an additional sprinkle of Pecorino Romano if desired.
Notes
Adjust the red pepper flakes to control the spice level.