In a medium bowl, mix flour, baking powder and salt.
In a large bowl, mix butter, shortening and sugar until light and fluffy with an electric mixer.
Beat in egg whites one at a time, scraping down the bowl after each addition. Add extracts and beat until well combined.
On low speed, alternate adding the four mixture and milk to the butter mixture, beginning and ending with the flour mixture.
Spray each of your 15 pans and divide batter evenly between the prepared pans.
Bake the cakes all together for 20 minutes. Remove and let cool.
Time to decorate!
Roll out yellow fondant and cut out little stars. Set aside.
Squeeze a few dollops of frosting onto a small round cake board and then stick the first cake onto the board.
Spread buttercream frosting on top of the first cake and then place another cake on top. Do this one more time and then frost the top and sides of the 3 cakes.
Repeat steps 2 and 3 three more times so that you have 4 frosted stacks on cake boards.
Use 2 of the 3 remaining cakes to make a small frosted stack on a cake board.
Stick the last cake to a small cake board and then frost it with blue frosting.
Press a dowel into a round Styrofoam base to create a foundation for the cakes.
8. Position a cake stack so that the hole in the middle of the cake board is lined up with the dowel and then guide the cake down to the base. Place 4 large straws into the cake to create more support. Make sure to cut the straws so they are not sticking out from the tops of the cakes.
Continue stacking cakes, stacking small stack and the blue cake last.
Use blue frosting in a decorating bag fitted with a #10 tip to pipe thick wavy lines onto the stacks, resembling the filling between each of the 15 layers on the Sleeping Beauty cake.
Place fondant stars evenly onto the sides of the top cake layer (the blue cake).
Use yellow frosting in a decorating bag fitted with a star tip to pipe draping “U” shapes in between each fondant star to connect them.
Pipe 15 small yellow dollops evenly around the outer-top of the blue cake and then stick a candle into each dollop.