Prepare three 9 inch cake pans by greasing them thoroughly and dusting them with flour. Discharge excess flour. Preheat the oven to 350°F or 180°C.
In a saucepan, melt the chocolate on low heat!
Combine the flour, baking powder, ground cinnamon, and salt in a medium-sized bowl and set aside.
Add the butter, sugar, oil, and vanilla extract to a large mixing bowl and beat together until light in color and fluffy, about 3-5 minutes. You can use a hand or a stand mixer for that.
Add one egg at a time, mixing until combined until you add the next egg. Scrape down the sides of the bowl as needed to get all the ingredients well combined.
Add the melted chocolate and mix until well combined.
Add half of the dry ingredients to the batter. Then, with a wooden spoon, carefully combine it with the mixture.
Slowly add the milk to the mixture until well combined.
Add the remaining dry ingredients and mix until well combined. Do not overmix the batter, or your cake will get a dome. You want an even cake without a dome.
Divide the batter evenly between the cake pans, and spread it with a spoon to achieve an even bake. Bake for 25-30min or until a toothpick comes out dry.
Take the pans out of the oven and allow them to cool for about 15 minutes. Then, carefully remove the pans and let the cakes cool completely on a cooling rack.