6 large eggs, separated
3/4 cup all-purpose flour
1 tablespoon baking powder
1/2 teaspoon salt
2 large oranges
2 tablespoons orange-flavor liqueur (optional)
1 32-ounce container ricotta cheese
1 8-once package cream cheese, softened
semisweet-chocolate mini pieces
3 tablespoons butter or margarine, softened
3 tablespoons milk
2 cups heavy or whipping cream
Early in day or day ahead: In large bowl, with mixer at high speed, beat egg whites until soft peaks form. Beating at high speed, gradually sprinkle in 1/2 cup sugar, 2 tablespoons at a time, beating well after each addition until sugar completely dissolves and whites stand in stiff peaks. Preheat over to 375F. In small bowl, with mixer at low speed, beat egg yolks, flour, baking powder , salt, 1/2 cup sugar, 1 teaspoon vanilla extract, and 2 tablespoons water until blended. Gently fold one-third beaten egg-white mixture into yolk mixture, then fold yolk mixture into remaining whites. Spoon batter into ungreased 10 by 3 springform pan. Bake 30 to 35 minutes, until cake is golden and top springs back when lightly touched with finger. Invert cake in pan on wire rack; cool completely.
Grate enough peel from oranges to measure 2 teaspoons peel; set aside. Squeeze enough juice from oranges to measure 1/3 cup juice. (If not using liqueur, increase orange juice to 1/2 cup.) Stir orange-liqueur into juice; set aside. In large bowl, with mixer at low speed, beat ricotta cheese, cream cheese, grated orange peel, 1 cup confectioners' sugar, and 1 teaspoon vanilla extract until smooth. Stir in 1/4 cup semisweet-chocolate mini pieces. With metal spatula, gently loosen cake and remove from pan. With serrated knife, cut cake horizontally into 2 layers. Brush orange-juice mixture evenly over cut side of both layers. Place 1 cake layer, cut-side up, on plate. Spoon ricotta-cheese filling on center of cake layer. Spread some filling out to edge, leaving center rounded to achieve a dome effect. Cut a wedge out of remaining cake layer; arrange wedge and rest of cake layer over filling. (Cutting wedge will allow cake layer to bend, without cracking, to fit over dome shape.)
In small bowl, with mixer at medium speed, beat butter or margarine, milk, 1 3/4 cups confectioners' sugar, and 3/4 teaspoon vanilla extract until smooth, adding more milk if necessary until frosting has an easy spreading consistency. In large bowl, with mixer at medium speed, beat heavy or whipping cream until soft peaks form; fold confectioners' sugar mixture into whipped cream. spread frosting over top and down side of cake. In 1-quart saucepan over low heat, heat 1/3 cup semisweet-chocolate mini pieces until melted. Spoon melted chocolate into small decorating bag with small writing tube (or, use paper cone with tip cut to make 1/8-inch diameter hole) Pipe chocolate on top of cake in a spiral design, starting in center and moving to edge of cake. Before chocolate hardens, quickly with tip of toothpick or small knife, draw lines in spoke fashion. Make spokes about 1 1/2 inches apart around edge of cake; alternate direction of each spoke, first from edge to center of cake, then from center to edge to make feather design. Refrigerate cake until filling is firm for easier cutting, about 3 hours.