For the Chocolate Cake Batter:

1. Preheat the oven to 350ºF. Grease and line three 8-inch cake pans.
2. In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, salt, and espresso powder (if using).
3. In another bowl, whisk together eggs, vegetable oil, buttermilk, sour cream, and vanilla extract.
4. Combine wet and dry ingredients, then add hot coffee and mix until smooth.
5. Divide batter into pans and bake for 30-35 minutes.
6. Let cakes cool before frosting.

For the Chocolate Syrup:

1. In a saucepan, whisk together sugar and cocoa powder. Add water and whisk over medium heat until boiling. Let cool.

For the Chocolate Buttercream:

1. Melt chocolate chips and heat cream. Combine and let cool.
2. Beat butter until creamy, then gradually add powdered sugar and cocoa powder.
3. Add cooled ganache and vanilla, beat until combined.

To assemble the cake:

1. Place one cake layer on a plate, brush with syrup, then spread buttercream. Repeat with remaining layers.
2. Frost top and sides of cake. Decorate with sprinkles.