1.Bring A Large Pot Of Lightly Salted Water To A Boil. Add The Angel Hair Pasta And Cook For 8 To 10 Minutes Or Until Al Dente. Once Done, Set Aside 1/2 Cup Of The Pasta Water, Then Drain The Pasta In A Colander In The Sink. Keep Warm. 2.While The Pasta Is Cooking, Melt The Butter In A Saucepan Over Medium Heat. Stir In The Onion, And Cook For 3 Minutes, Then Stir In The Garlic, And Continue Cooking Until The Onion Has Softened And Turned Translucent, 1 To 2 Minutes More. 3.Pour In The Heavy Cream, And Stir In The Parmesan Cheese, Basil, Salt, And Pepper. Bring To A Simmer, Then Reduce Heat To Medium-Low, And Simmer For 2 Minutes. Dilute With The Reserved Pasta Water If The Sauce Is Too Thick For Your Taste. Pour The Sauce Over The Angel Hair Pasta To Serve.