Preheat oven to 350 degrees. Line a 9 x 13 baking pan with parchments paper. Add 10 cupcake papers to a cupcake tin.
Mix the buttermilk, vanilla, orange blossom and sour cream in a glass and set aside.
Sift the dry ingredients (except the sugar) together and give a good whisk to mix well.
Cream the butter and sugar together in a stand mixer fitted with a paddle attachment for approximately 4 minutes on medium.
Add the eggs one at a time making sure each is incorporated well before adding the next.
Add the flour mixture mixture in three batches alternating with the milk mixture. Making sure you start and end with the flour mixture. Do not over mix, just beat until combined.
Mix in the pumpkin puree. Scrape down the sides of the bowl and make sure the pumpkin is well incorporated.
Pour batter into cake pan and excess into cupcakes. Bake the cake at 350 degrees for about 30 minutes or until the center is set.
Bake the excess cupcakes for about 15 to 20 minutes at the same temperature.
Allow cake to rest for about 10 minutes, then invert onto either a wire rack or a large plate. Move to parchment paper, allow to cool to room temperature.
Set the excess cupcakes aside to cool.
For Vanilla Pudding:
Whisk sugar, cornstarch, and salt in a saucepan.
Add milk into the sugar mixture. Stir until a paste. Combine milk and egg yolks.
Cook the mixture on a low heat, while stirring continuously. Let the mixture thicken and don't over boil. Turn off the heat. Add butter, rum and vanilla.
Transfer mixture to a bowl. Create an airtight seal with plastic wrap. Move to the refrigerator for about an hour until chilled.
For the Browned Buttercream:
Cook over medium heat, while stirring frequently until butter is golden brow. Transfer to bowl and whisk in spices. Allow to cool to room temperature.
In a standing mixer fitted with a paddle attachment, beat the butter on low speed. Add sifted confectioners' sugar. Continue mixing on low. Drizzle in vanilla and cream. Mix until desired consistency is reached.
For the Assembly:
Use a round dowel or any handy kitchen tool to poke holes into the cake.
Use a knife or offset spatula to spread the pudding over the sheet. Press into the holes. Remove excess with a spatula and allow to soak in.
Smooth on the buttercream.
Video
Notes
You can substitute whole milk yogurt for the sour cream if desired, I do it all the time and can’t really tell the difference.
If you don’t want to brown the butter you can make use regular room temp butter, Just add the spices when it's being creamed and you'll still enjoy the flavor.
This cake is amazing even without the pudding so go ahead and make a regular sheet cake if you're short on time.
MIX that meringue buttercream RIGHT before use!!! It loses consistency quickly.
Hate cloves, nutmeg or some other spice in this recipe? Skip it and use which ever spices you prefer!