Begin by preheating your oven to 350°F (175°C). Thoroughly grease a standard bundt pan with shortening, ensuring all crevices are coated, then dust lightly with flour, shaking out the excess. This prevents sticking and ensures a smooth release.
In a large mixing bowl, combine the sugar, flour, baking soda, salt, and cinnamon. Set this dry mixture aside for now.
Melt the butter over medium heat in a medium saucepan. Once melted, whisk in the oil, cocoa powder, and water. Bring the mixture to a gentle boil while stirring constantly to blend the ingredients.
Carefully pour the heated cocoa mixture into the bowl with the dry ingredients. Stir until just combined.
Add the buttermilk, eggs, and vanilla to the mixture. Using a whisk, blend everything together until smooth. Gently fold in the mini chocolate chips, if you're using them.
Transfer the cake batter into the prepared bundt pan, ensuring it's evenly spread. Bake for 45-55 minutes, or until a toothpick inserted into the center emerges with just a few moist crumbs.
Once done, allow the cake to cool in the pan for 5 minutes before inverting it onto a wire rack to cool completely.