Whisk together first 5 ingredients in a large saucepan. Cook over medium heat, whisking constantly, until mixture boils. Boil, whisking constantly, 1 minute. Remove from heat, and stir in butter and vanilla.
Line bottom of a trifle bowl or large clear bowl with one-third of banana slices and one-third of pudding. Repeat layers twice, ending with pudding. Cover and chill 8 hours.
Beat whipping cream at medium speed with an electric mixer until foamy; gradually add powdered sugar, beating until soft peaks form. Spread evenly over pudding. Serve with Sugar Biscuits.