Pre-heat oven to 350*F. Line a 9"x 9" cake pan with a piece of parchment paper, leaving a bit of an overhang (so you can pull out the cake after it's baked). Lightly butter the two sides of the pan not covered by parchment.
In a large bowl, whisk together sugar, flour, cocoa powder, baking powder, baking soda and salt.
Add egg and whisk to combine, then add milk, oil and vanilla and stir well.
Add hot water (or hot coffee) and blend until fully incorporated. The batter will be very thin, this is right.
Pour batter into prepared pan and bake 22-28 minutes, or until a toothpick inserted into the center of the cake come out clean.
While the cake cools, use a pastry brush to brush the top of the cake with the Grand Marnier.
Make the frosting
In the bowl of an electric mixer, blend the soften butter until smooth. Add cream cheese and blend until fully combined.
While mixing, slowly add powdered sugar, then extracts. Add a drop of orange food coloring, if desired. Blend until smooth. You may need to stop the mixer and scrape down the sides.
Make the ganache
Chop chocolate, or use good quality chocolate chips, and add to a medium bowl.
Heat cream in the microwave until hot, but do not let it boil.
Pour hot cream over chocolate and allow it to sit, undisturbed 1-2 minutes.
Stir until smooth, then move to the fridge to firm up a bit.
Assemble the cake
Remove (fully) cooled cake from the pan by pulling up on the exposed parchment paper. Place cake on a cutting board. Cut cake in half, so that you have two 4.5" x 9" rectangle pieces.
Move one of the pieces of cake to a wire cooling rack with a baking sheet under it (this will be needed shortly, when frosting with ganache).
Spread the orange frosting onto the cake (on the cooling rack), using an offset spatula. Top with the second piece of cake.
Check on the ganache, it should be thickened slightly, but still pour-able. Pour some of the ganache onto the cake and use an offset spatula to spread it down the sides of the cake. Once the cake is covered with a thin layer of ganache, move the entire cake (on the rack) to the freezer for 5-10 minutes to allow the ganache to set up a bit.
Once the first layer of ganache has set, use 2 large spatulas to move the cake to a serving platter of your choice. Pour a second layer of ganache over the cake. You will need to experiment with how thick or thin you want the ganache. You can chill it in the fridge to thicken, or microwave (on 50% power) for short periods to thin it. For my cake the top layer of ganache was thick enough that I was able to add some texture to the very top of the cake with an offset spatula (spreading from side to side).
Garish generously with Candied Orange Peel.
For the best flavor, be sure to use pure extracts and good quality cocoa powder and chocolate.