1.Cook Pasta In A Large Pot Of Boiling Water Until Al Dente; Drain. 2.Meanwhile, Melt Butter In A Large Saucepan. Saute Onion And Garlic Over Medium Heat Until Tender. Add Shrimp; Saute Over High Heat For 1 Minute, Stirring Constantly. Stir In Half-And-Half. Cook, Stirring Constantly, Until Sauce Thickens. 3.Place Pasta In A Serving Dish, And Cover With Shrimp Sauce. Sprinkle With Black Pepper And Parmesan Cheese. Garnish With Parsley And Lemon Slices.