Prepare the Cornstarch Slurry: In a small bowl, mix 1 tablespoon of cornstarch with 2 tablespoons of cold water until smooth.
Melt Butter: In a pan over medium heat, melt the butter and add the minced garlic. Sauté for about 1 minute until fragrant.
Add Lemon Components: Stir in the lemon zest and juice.
Incorporate the Slurry: Whisk the cornstarch slurry into the pan, ensuring it's well combined.
Add Water and Cheese: Pour in ½ cup of water and gradually add the grated Parmesan, stirring continuously until the cheese melts and the sauce thickens.
Season and Finish: Add black pepper, red pepper flakes (if using), and chopped parsley. Toss with your cooked pasta and serve immediately.