To make the frozen mousse, add egg yolks and sugar to a bowl and whisk. Add cornstarch, vanilla, orange juice, and orange liqueur and whisk to incorporate. Put bowl in a bain marie and cook until temperature reaches 180 F (80 C). Remove from heat and beat until mixture has cooled. Put over top of bowl of ice to cool. Beat cream and orange zest until stiff peaks form. Gently fold cream into orange mixture, add a bit at a time. Pour into a 20 centimeter glass bowl lined with plastic wrap. Cover and freeze.
To make the cake, preheat oven to 350 F (180 C). Whisk together egg yolks, milk, vegetable oil, and vanilla seeds. In a separate bowl, sift cake flour, 1/4 cup (60 milliliters) sugar, baking powder, and salt. Pour flour mixture into egg yolk mixture and stir to combine. Beat egg whites until soft peaks form. Add remaining sugar slowly, and continue beating until stiff peaks form. Fold egg whites into egg yolk mixture. Pour into a 20 centimeter pan lined with parchment paper. Bake 25-30 minutes until toothpick inserted into the centre comes out clean. Let cool. Fit into bowl with mousse, cutting away excess over the top of the bowl, and let freeze four hours or more.
To make the meringue, whisk together egg whites, sugar, and salt in a bain marie. Whisk until temperature reaches 150 F (65 C). Take off the heat, add cream of tartar and orange zest and beat until egg whites are thick and glossy.
Release mousse-cake from bowl. Spread meringue over cake. Use a confectionary torch to brown the meringue. Measure 56 grams of orange liqueur. Place in a small saucepan and heat over medium heat until it starts to simmer. Using a long-handled match, light liqueur on fire. Pour over Baked Alaska. Let flame die out – this should take a few seconds.