Preheat oven to 350 degrees. Line three 9-inch round cake pans with waxed paper, then grease the waxed paper.
Sift flour with cocoa powder, baking powder and salt. Set aside.
In a small mixing bowl, combine 3/4 cup butter, 3/4 cup sugar and 6 egg yolks. On high speed of an electric mixer, beat until light and fluffy. Stir in 1 tablespoon vanilla.
Add flour mixture alternately with milk, beginning and ending with flour. Spread batter into the prepared pans, dividing evenly; set aside.
In a clean bowl with clean beaters, beat 6 egg whites until soft peaks form. Gradually beat in remaining 1 cup sugar; beat until stiff but not dry. Dividing evenly, spread meringue over the batter in each pan.
Bake for 30-35 minutes or until cake is done and meringue is lightly browned. Let cool in pans 10 minutes. Carefully remove from pans; peel off paper. Cool layers completely on wire racks, meringue side up.
Meanwhile, prepare orange curd: In the top of a double boiler, stir together 1/2 cup sugar and cornstarch. Stir in water, orange juice and orange zest. Blend in 4 beaten egg yolks.
Cook over hot (not boiling) water, stirring constantly, until mixture thickens, about 8 minutes. Remove from heat. Stir in 2 teaspoons vanilla. Cover with waxed paper; let cool completely.
To assemble: Place a cake layer, meringue side up, on a cake plate. Spread a third of the orange curd over the meringue. Repeat twice, using remaining layers and curd. Garnish with whipped cream and sliced almonds, if desired.
Note: If desired, replace 1 tablespoon of orange juice with 1 tablespoon orange liqueur.