01 Adjust your oven rack to the 2nd level and pre-heat your oven to 350ºF.
02Generously spray your 9” x 13” pan with a flour-based baking spray.
03 In a medium sauce pan, add the butter, cocoa, and water and bring to a boil. Carefully remove from the heat and pour into a large mixing bowl or a mixing bowl that’s part of a stand mixer fitted with a paddle attachment.
04Add the vanilla extract, buttermilk, flour, cinnamon, baking soda, baking powder, salt, eggs, and sugar to the mixing bowl, and using a mixer or stand mixer, beat on medium speed until fully combined. Scrape down the sides of the bowl as needed. The batter will be a thicker consistency, but still runny and easy to pour. Be careful not over mix the cake batter.
05Pour the batter into the 9” x 13” cake pan and bake at 350ºF for 35-40 minutes or until an inserted toothpick into the center of the cake comes out clean.
06Remove from oven and allow to cool completely before topping with the Chocolate Ganache Frosting.
07To make the Chocolate Ganache Frosting, add the semi-sweet chocolate chips to a medium size mixing bowl. Set aside.
08Heat the heavy whipping cream in a small saucepan until it boils, then pour it over the chocolate chips and let it sit, covered for 2-3 minutes.
09Whisk the mixture until it’s smooth and creamy, then cover with plastic wrap and refrigerate until the frosting has completely cooled (about 1 hour).
10Using a hand-held mixer or stand mixer fitted with a whisk attachment, beat the frosting for 2-3 minutes until it’s nice and fluffy. Spread onto the Chocolate Sheet Cake, decorate with sprinkles (optional), then serve.