Prepare and bake the Pastry Crust in a 9-inch round removable-bottom tart pan. Cool crust completely on a wire rack.
Peel and section oranges over a bowl; squeeze membranes to extract juice. Set 2 cups sections aside; reserve 1/2 cup juice. Discard membranes.
Combine sugar, cornstarch, and salt in a small saucepan; gradually add reserved juice, stirring with a whisk until blended. Bring to a boil over medium heat, stirring constantly. Reduce heat to low; cook 1 minute. Remove from heat; stir in vanilla. Cool, stirring occasionally.
Place marmalade in a small microwave-safe bowl, and microwave at HIGH 30 seconds or until marmalade melts. Spread marmalade in bottom of prepared crust. Arrange 1 cup orange sections on top of marmalade; spoon 1/3 cup orange filling over sections. Top with remaining orange sections and orange filling. Cover and chill at least 4 hours.