Pre-heat oven to 375o F.
In a small bowl with mixer at high speed, beat egg whites until soft peaks form. Gradually sprinkle in 1/2 cup sugar, beating until sugar completely dissolves and whites stand in stiff peaks. In large bowl, using same beaters and with mixer at low speed, beat egg yolks, flour, baking powder, salt, remaining 1/2 cup sugar, 1 TSP vanilla, and 2 TBSP water until blended. With rubber spatula, gently fold beaten egg whites into egg yolk mixture, one third at a time.
Spoon batter into ungreased 10 inch by 3 inch springform pan. Bake 30 to 35 minutes until cake is golden and top springs back when lightly touched. Invert cake in pan on wire rack. Cool completely in pan.
From oranges grate 2 TSP peel and squeeze 1/3 cup juice. Stir liqueur into juice. Set aside. In large bowl, with mixer at low speed, beat ricotta, cream cheese, grated orange peel, confectioners sugar, and remaining 1 TSP vanilla extract until smooth. Stir in 1/4 cup semi-sweet chocolate chips. With metal spatula, loosen cake from edge of pan. Remove pan side. Loosen cake from pan bottom. Remove pan bottom. With serrated knife, cut cake horizontally into 2 layers. Brush orange juice mixture evenly over cut side of both layers.
Place bottom cake layer, cut side up, on cake 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. Prepare Vanilla-Cream frosting. Spread over top and down side of cake.
In heavy small saucepan over low heat, heat remaining 1/3 cup chocolate chips, stirring frequently, until melted and smooth. Into waxed-paper cone, spoon melted chocolate. Cut tip to make 1/8 inch hole. Pipe melted chocolate on top of cake in concentric circles, starting in center and moving to edge of cake. Before chocolate hardens, quickly with tip of tooth pick, draw lines in spoke fashion about 1-1/2 inch apart around edge of cake. Alternate direction of each spoke, first from edge to center of cake, then from center to edge. Refrigerate cake until filling is firm for easy cutting, about 3 hours.
In small bowl, with mixer at medium speed, beat 3 TBSP softened margarine, 3 TBSP milk, 1-3/4 cups confectioners sugar, and 3 TSP vanilla extract until smooth, adding more milk if necessary until mixture has an easy spreading consistency. In large bowl, using same beaters and with mixer at medium speed, beat 2 cups heavy or whipping cream until stiff peaks form. Fold confectioners sugar mixture into whipping cream