Preheat oven to 350°F.

Using vegetable shortening or cooking spray, grease two 9" round cake pans, then place a circle of parchment to line the bottom of each.

Whisk together vegetable oil, eggs, orange juice, orange zest, milk, hot coffee, and vanilla.

In a separate bowl, stir together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

Slowly add dry ingredients to wet and mix just until all ingredients are combined (but in order to keep the cake light and fluffy, don't overmix).

Divide batter equally between two greased and lined cake pans.

Bake on middle rack for 25 minutes or until a toothpick inserted in the center comes out clean.

Let cool a few minutes, then turn out onto a plate, remove the parchment from the bottom of each cake, and flip right side up onto cooling racks to cool completely.

While the cakes are cooling, make the chocolate orange buttercream frosting.

Break the chocolate bar into small pieces and add to a microwave-safe bowl, along with the heavy cream.

Microwave for 30 seconds, then stir. Then microwave in 15-second increments, stirring after each one, until smooth. This should take about 1-½ to 2 minutes total.

Once the chocolate and cream are melted together, let it cool on the counter for a few minutes while you start the frosting mixture.

Whisk softened, room temperature butter until smooth (scraping down sides of bowl as necessary).

Add powdered sugar, 1 cup at a time, blending until smooth between each one.

Next, add the orange juice, vanilla extract, cocoa powder, salt, and orange zest, and mix well.

Finally, add the melted chocolate and mix one more time until the frosting is smooth and fluffy.