To prepare cranberries, combine 3/4 cup sugar, orange juice, and Grand Marnier in a medium saucepan over medium-high heat; cook 3 minutes until sugar dissolves, stirring occasionally. Add cranberries to pan; bring to a boil. Reduce heat; simmer 8 minutes or until cranberries pop. Spoon mixture into a bowl; cover and chill.
To prepare pastry cream, combine 1/2 cup sugar and cornstarch in a medium, heavy saucepan over medium heat. Gradually add milk to pan, stirring with a whisk until blended; bring to a boil. Cook 1 minute, stirring constantly. Remove from heat. Gradually add half of hot milk mixture to eggs, stirring constantly with a whisk. Return milk mixture to pan; cook over medium heat 1 minute or until thick, stirring constantly. Remove from heat. Stir in vanilla and salt. Place pan in a large ice-filled bowl until custard cools to room temperature (about 25 minutes), stirring occasionally.
Arrange half of cake cubes in the bottom of a 2-quart trifle dish. Spoon 1 1/2 cups cranberry mixture over cake; top with 1 1/2 cups pastry cream. Repeat layers. Garnish with rind. Cover loosely with plastic wrap, and chill at least 4 hours.