Heat oven to 350 degrees F. Coat three 8 x 2-inch round straight-sided layer cake pans with nonstick vegetable-oil cooking spray. Line with waxed paper. Coat paper with spray.
Whisk together flour, baking powder and salt in large bowl.
On medium speed, beat butter in large bowl until smooth and creamy, about 1 minute. Add sugar and beat until light and fluffy, about 2 minutes. Add eggs, one at a time, beating well after each addition. Add vanilla and beat 1 minute.
On low speed, beat flour mixture into butter mixture in 3 additions, alternating with 1-1/4 cups milk, ending with flour. Beat on medium speed for 2 minutes.
Pour 1-1/2 cups batter into one of prepared pans. Pour two 1-1/2-cup portions of batter into 2 separate bowls. Tint batter in one bowl pink. Pour into a prepared pan. In small measuring cup, mix together remaining 2 tablespoons milk and cocoa powder until dissolved. Beat into remaining bowl of batter. Pour into the remaining prepared pan.
Bake in 350 degree F oven for about 20 minutes or until a wooden pick inserted in centers of cakes comes out clean. Cool cakes on wire rack about 10 minutes. Turn cakes out of pans onto wire racks; remove waxed paper; let them cool completely.
Beat heavy cream in a medium-size bowl on medium-high speed until foamy. Add vanilla and sugar, 1 tablespoon at a time, beating until medium-stiff peaks form. Cover the bowl and refrigerate the filling until ready to use.
Heat cream in medium-size saucepan to boiling. Pour over chopped chocolate in heat-proof bowl; stir until smooth. Beat on medium speed until cool and fluffy, 5 to 7 minutes; do not overbeat or frosting will be difficult to pipe into smooth teardrops. Cover; set aside.
Place wooden picks around side of one cake layer, measuring half way up side. Using picks as guide, slice cake in half horizontally. Repeat with 2 other cakes for total of 6 layers. Place one chocolate cake layer on cake plate. Spread 1/3 cup filling over top. Place a pink layer on top. Spread pink layer with 1/3 cup filling. Top with a vanilla layer. Cover with 1/3 cup filling. Repeat with remaining 3 cake layers and filling, ending with vanilla cake layer, no filling on top. Cover sides of cake with ganache frosting. Using pastry comb, make decorative pattern on frosting. Spread thin layer of ganache over top of cake. Spoon remaining ganache into pastry bag fitted with coupler and 3/8-inch plain round tip.
Stir marshmallow fluff and 1 cup confectioners' sugar in medium-size bowl with wooden spoon until thick mass forms. Knead in bowl until mass comes together. Turn out onto work surface; knead until smooth, working in more confectioners' sugar. Dust work surface and rolling pin with cornstarch. Shape marshmallow mixture into a disk. Roll out to 1/8-inch thickness. Cut into strips, 1-1/2-inch wide. Crimp like a pie crust to form a collar with a wavy design. Place around top edge of cake so it overhangs a little.
Using pastry bag filled with the ganache, pipe teardrops over the entire top of the cake, in an orderly pattern. Overlap slightly so the bottoms of the teardrops are not completely visible. Replace 3/8-inch tip with small round tip, and pipe small dots of the ganache all around the bottom of the cake.
Using small sieve, carefully dust the confectioners' sugar evenly over the ganache teardrops, being careful not to dust the marshmallow collar. Refrigerate the cake for at least 1 hour before serving.