Preheat oven to 350 F. Spray two 9 inch round baking pans with nonstick spray, or butter and flour the pans, or line the baking pans with parchment paper, or line with aluminum foil and spray with non-stick spray; set aside. Fasten the wet cake strips around the baking pans if you have them.

To a bowl of a stand mixer add the eggs and sugar, then whip for about 5 minutes or until fluffy. Whisk in the oil and the pumpkin puree. Next, sift the flour, baking powder, and baking soda, salt and cinnamon (if using) and carefully fold it in. 
Lastly fold in 1/2 cup sour cream until smooth batter forms. 

Divide the batter between the two prepared pans evenly and bake for about 45 minutes or until a toothpick inserted in the center comes out clean. Do not check before 30 minutes. 

Remove cakes from the oven and allow to cool for about 10 minutes before running a knife around the inside of the baking pan to loosen the cake away from the sides. Transfer to a cooling rack and cool completely (very important).

If you did not use cake strips, cut off the domed tops of the cake. Then, with a serrated knife cut each cake layer into two horizontally. 

Whip the butter for about 5 minutes, scraping down the sides several times. Add the condensed milk and whip until incorporated. Next add the cream cheese, powdered sugar, and the vanilla extract and whip until fully incorporated and smooth.

Microwave the heavy whipping cream until boiling hot, add the chocolate chips and allow to sit for 1 minute, then stir until smooth. Bring to room temperature. Place into a sandwich size ziplock bag or a pastry bag. Trim the corner to drizzle right before assembling the cake.

Use a maple leave cutter like the one sold HERE and cut out about 10 maple leaves. Brush the puff pastry leaves with egg wash and sprinkle with sugar. Bake in preheated to 400F oven for about 10 minutes or until puffed up and golden. Allow to cool completely.

Reserve 1 1/2 cup of frosting for covering the outside of the cake and set aside. 

Place a small dab of frosting onto the cake platter and press the first cake layer to adhere. Add 1/3 of the frosting and spread around into an even layer. Drizzle couple tablespoons of cooled chocolate ganache on top. Repeat with the remaining pumpkin cake layers and the frosting. 

If using the puff pastry maple leaves for decoration, reserve about 3-4 tablespoons of cream for adhering the cookie leaves to the cake. Otherwise, use all reserved cream to cover the cake, smooth it with a spatula or a cake scraper, then pipe a "dot" border around the bottom of the cake.

If the remaining ganache has thickened too much, microwave it in 2-3 second intervals until pourable consistency. Do not make the ganache warm or it will melt the buttercream as you pour it. 

Pour the ganache in the middle top of the cake and spread it around with an offset spatula, bringing it to the edges until it just drizzles over the sides of the cake. 

If decorating with the cookie leaves, pipe small dollops of cream in a moon shape pattern, then lean the puff pastry maple leaves against these piped dollops.

Refrigerate the cake for about 4-5 hours before cutting. Leave at room temperature for about 1 hour before serving.