Bring a large pot of salted water to a boil and cook pappardelle until al dente according to package instructions. Reserve some pasta water before draining. This starchy water helps bind sauce later. Drain pasta and set aside briefly.
Heat olive oil and butter in a skillet over medium heat until melted. Add minced garlic and sauté gently until fragrant without browning. Slow cooking keeps garlic sweet and prevents bitterness.
Pour heavy cream into the skillet and allow it to simmer gently for a few minutes. Stir occasionally until slightly thickened. Add lemon zest and lemon juice, balancing creaminess with citrus brightness.
Lower heat and stir in freshly grated Parmesan cheese gradually. Season with salt, pepper, and red pepper flakes if using. Sauce should become creamy and smooth without clumping.
Add cooked pasta directly into the sauce along with a splash of reserved pasta water. Toss gently until noodles are fully coated and sauce thickens beautifully. Adjust consistency with extra pasta water if needed.
Turn off heat and taste for seasoning adjustments. Serve immediately with extra cheese, herbs, and lemon zest on top. Fresh garnish enhances both presentation and flavor.