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.