Cream, in this case, half-and-half, adds an ineffable, luxurious quality to any pasta sauce. It works its magic here in a simple, summery combination that is as pretty as it is comforting. A big bowl of this on a buffet table alongside a platter of roasted chicken or a selection of vegetable salads, a wonderful bread or two, a cut of cheese, and you have the makings of a feast. Another advantage: Both the pasta and the base of the sauce can be made in advance.