In a small bowl, melt white chocolate. To do this I place in microwave on 50% power in 30 second intervals, stirring after each interval. Set aside to cool for about 5 minutes before using in frosting.
Beat together butter and shortening until light and fluffy, about 4-5 minutes.
Then, on medium speed, beat in powdered sugar about 1/2 cup at a time. Scrape down sides with spatula as needed.
Next, beat in vanilla, pumpkin pie spice, nutmeg, cinnamon and salt.
After this, slowly mix in melted chocolate. Once incorporated beat on high speed for about 30 seconds to mix thoroughly.
Mix in 3-4 tablespoons of heavy cream to reach desired consistency.
If needed, level cakes. As there is not much leavening and the cake does not rise much, I find I generally do not have to do this.
Place one layer of a cake on a cake board. Put frosting in a pasty bag and pipe boarder along outside of one layer. Fill inside boarder with desired amount of pralina filling (I use about 1/4 of the mixture for each layer). Place a second layer on top, and repeat. Finally, place third layer on top.
churro cake filling
Use frosting to lightly frost outside of cake (this is a crumb layer). Place cake in fridge for about 15 minutes, then finish frosting.
Place dark chocolate chips in a heat safe bow. Place heavy cream in microwave safe bowl and heat until cream starts to boil, about 1 minute. Pour heated cream over chocolate and cover bowl in plastic wrap. Let set for 5 minutes, then whisk until smooth. Pour over top of cake and let run down the sides.
Let ganache sit for at least 5 minutes before you decorate the top with additional buttercream.