How to Make It
Prepare Filling: Bring first 3 ingredients and 3 cups cranberries to a boil in a saucepan over medium-high heat; reduce heat to low, and boil, stirring often, 5 to 6 minutes or until berries begin to pop. Remove from heat, and stir in remaining 1 cup cranberries. Transfer mixture to a bowl; cool completely (about 30 minutes). Cover and chill 8 to 24 hours.
Meanwhile, prepare Custard. Whisk together brown sugar, cornstarch, and salt in a large heavy saucepan; whisk in milk and 1 1/2 cups cream. Bring mixture to a boil over medium heat, whisking constantly. Boil 1 minute, whisking constantly. Remove from heat.
Whisk in butter and next 3 ingredients. Transfer mixture to a medium bowl, and place plastic wrap directly on mixture (to prevent a film from forming). Cool completely (about 30 minutes). Chill 8 to 24 hours.
Assemble trifle. Layer about one-third of cake cubes in a 4-qt. bowl. Top with one-third each cranberry filling and custard. Repeat layers twice.
Prepare Topping: Beat vanilla extract and 2 cups heavy cream at medium-high speed until foamy; gradually add powdered sugar, beating until soft peaks form. Dollop over trifle. Serve immediately, or chill up to 8 hours.