Orange Custard Tart with Chocolate Shortbread Crust

FOR CRUST: Preheat oven to 325 degrees F. Using an electric stand mixer and paddle attachment, beat butter and sugar in large bowl until light and fluffy. Add cocoa and salt. Beat on low speed just until blended. Add flour and beat until dough forms. Gather dough into ball. Press dough evenly over bottom and sides of 14 x 4 1/2-inch rectangular tart pan with removable bottom. Chill 15 minutes. Bake until edges are firm but center is still slightly soft, about 30 minutes (the crust will firm as it cools). Cool crust completely.

DO-AHEAD TIP: Crust can be made 1 day ahead. Keep tart in pan and wrap with plastic. Store at room temperature.

FOR CUSTARD: Whisk sugar, egg yolks, cornstarch, orange peel and salt in heavy medium saucepan until thick and smooth. Whisk in milk. Using rubber spatula, stir over medium heat until mixture thickens and bubbles burst atop custard, about 4 minutes. Cook custard, whisking constantly, 1 minute longer. Cool slightly, stirring often. Place plastic wrap directly onto surface of custard. Refrigerate until cold.

Using electric stand mixer and whisk attachment, beat cream in large bowl just until firm peaks form. Using rubber spatula, fold one-third of whipped cream into custard. Spoon custard into prepared tart crust, spreading evenly. Spoon remaining whipped cream atop custard.

Sprinkle shaved chocolate over whipped cream and serve.