In a large pot, combine the spaghetti noodles, water, minced garlic, salt, and black pepper.
Bring the mixture to a boil over medium-high heat, stirring occasionally to prevent the noodles from sticking.
Reduce the heat to medium and cook the noodles until al dente, about 8-10 minutes, stirring frequently.
Once the noodles are cooked and most of the water is absorbed, reduce the heat to low.
Add the unsalted butter and heavy cream to the pot, stirring until the butter is melted and the sauce is creamy.
Stir in the grated Parmesan cheese and crushed red pepper flakes until the cheese is fully melted and the sauce is smooth.
Taste and adjust seasoning with additional salt or pepper if desired.
Remove the pot from heat and sprinkle the chopped fresh parsley over the noodles.
Serve immediately, garnished with extra Parmesan cheese if desired.