Cake: Preheat oven to 180 degrees C. Lightly grease and flour two 20cm round cake tins.
In a small bowl stir together flour, poppy seeds, baking powder, salt and nutmeg; set aside.
In a large bowl, cream together the butter and sugar until fluffy. Beat in eggs one at a time then add the orange zest and vanilla. Stir in the flour mixture, beating at low speed until well blended.
Divide the batter equally into cake tins. Bake in the preheated oven for 20 to 30 minutes. Allow to cool.
Filling: Combine the icing sugar, butter, egg yolks and vanilla. Beat on medium high speed until light and fluffy; about 2 to 3 minutes.
Orange Glaze: In a saucepan, combine orange juice, sugar, cornflour and orange zest. Cook over medium heat stirring constantly until mixture thickens and comes to a boil. Set aside to cool.
To Assemble: Cut each cooled cake layer in half horizontally. Stack the 4 cake layers together with about 1/3 cup of filling spread between each layer. Spread the filling also on the sides of the cake, but not the top. Refrigerate for 2 hours.
Spread the cooled (but not cold) glaze over top of cake and garnish with curls of orange peel. Store cake in refrigerator until served.