In a medium saucepan, combine sugar and cornstarch. Add half-and-half and egg yolks, whisking to combine.
Bring to a boil over medium-high heat; cook for 1 minute, whisking constantly. Remove from heat and gradually whisk in butter until butter is melted. Stir in sour cream and vanilla. Cool mixture slightly; cover and chill completely.
In 4 (1-pint) re-sealable jars, layer custard mixture, bananas, and vanilla wafers; repeat layers as desired. Seal jars with lids, and refrigerate. When ready to serve, top pudding with sweetened whipped cream, if desired.
