Combine first 6 ingredients in top of a double boiler, stirring with a whisk. Cook over medium-high heat 3 minutes or until mixture thickens. Transfer to a medium bowl to cool.
Beat whipping cream at high speed with an electric mixer until soft peaks form; fold into lemon mixture.
Layer lemon cream, Blueberry Syrup, cake, and blueberries in 8 parfait glasses. Garnish, if desired.