Begin by preheating your oven to 350°F. Grease an 8-inch round cake pan using butter, baking spray, or vegetable oil. Place a parchment paper at the bottom for easy removal.
In a mixing bowl, sift together 2 cups of flour, 1 cup of granulated sugar, ½ cup of unsweetened cocoa powder, 1 tablespoon of cinnamon, 1½ teaspoons of baking powder, 1½ teaspoons of baking soda, and ½ teaspoon of salt. Whisk the dry ingredients to combine.
In a separate bowl, combine three-quarter cups of melted butter, a quarter cup of oil, 2 eggs, vanilla, and buttermilk. Whisk the wet ingredients until well combined.
Pour the dry ingredients mixture into the wet ingredients and mix until thoroughly combined.
Pour a cup of boiling water into the batter; this will result in a runny batter, which is normal.
Pour the batter into the greased cake pan and bake for 35 minutes or until a toothpick inserted in the center comes out clean.
Once baked, let the cake cool in the pan for about 15 minutes. Carefully invert the cake onto a flat plate or cake board, remove the parchment paper, and your moist chocolate cake is ready to be served.