FOR THE CAKE: Begin early in day or day ahead to make Cannoli Cake.
Preheat oven to 375°F In 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, and 1 teaspoon vanilla, and 2 Tablespoons 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.
FOR BRUSHING CAKE LAYERS: From oranges, grate 2 teaspoons peel (use the rest of peel for the filling) and squeeze 1/3 cup juice (IF NOT USING LIQUEUR, INCREASE JUICE TO 1/2 CUP). Stir liqueur into 1/3 cup juice; set aside.
FOR THE FILLING: In large bowl, with mixer at low speed, beat ricotta, cream cheese, rest of the grated orange peel, confectioners’ sugar and 1 teaspoon vanilla extract until smooth. Stir in 1/4 cup semisweet-chocolate mini pieces.
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 a center rounded to achieve a dome effect.
Cut a small wedge out of remaining cake layer; and gently rest cake layer over filling. (Cutting wedge will allow cake layer to bend, without cracking, to fit over dome shape.).
PREPARE VANILLA-CREAM FROSTING: In small bowl, with mixer at medium speed, beat 3 Tablespoons margarine or butter, softened, 3 Tablespoons milk, 1 3/4 cups confectioners’ sugar, and 3/4 teaspoon 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 whipped cream. Spread over top and down side of cake.
In a heavy small saucepan over low heat, heat remaining 1/3 cup mini pieces, stirring frequently, until melted and smooth.
Into waxed-paper cone, spoon melted chocolate. (Or, use small decorating bag with small writing tube.) With chocolate, make feather design.
Refrigerate cake until filling is firm for easier cutting, about 3 hours.
TO MAKE WAXED-PAPER CONE: Cut square of waxed paper; fold in half into triangle. Lay triangle on flat surface so wide side is at top. Fold left-hand corner down to center point. Take right-hand corner; wrap it completely around folded left-hand corner, forming cone. Both corners meet at center point of original triangle. Fold in these ends twice to hold together. Fill cone two thirds full; fold top over.
MAKING FEATHER DESIGN: Piping circles on Cake: Using paper cone with tip cup to make 1/8 inch diameter hole, pipe melted chocolate on top of cake in concentric circles, starting in center and moving to edge of cake. Start with small circle in the middle of cake and go around each circle to the edge. This should be 6 circles.
Drawing spokes towards center: Before chocolate hardens, quickly with tip of toothpick or small knife, draw lines in spoke fashion, 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.
Completing feather design: Continue around top of cake, alternating direction of each spoke to make attractive feather design. 16 servings.