Preheat oven to 400℉. Grease a large sheet pan and set aside.
Mix the unsifted flour, sugar, and baking soda in a large bowl. Set aside.
In a medium saucepan, add stick of butter or margarine, Crisco, cocoa powder, water, salt, and cinnamon. Bring to a boil while mixing.
Boil cocoa mixture for about 2 minutes, being careful not to burn it.
Pour cocoa mixture over your dry ingredients from Step 2, and mix to combine.
Add beaten eggs, buttermilk, and vanilla extract, and mix to combine.
Pour the cake batter into the greased sheet pan, spreading it around with a spatula so that the batter is in an even layer. *See notes on sheet pan size.
Bake at 400°F for approximately 14-16 minutes.