Preheat Oven to 350°F. Place a rack in the center of the oven. Place another rack on the very bottom.
Spray or grease an 8 inch cake pan. Line the very bottom with parchment paper and then spray or grease the paper. *If you don’t have an 8” cake pan, a 9” will work. The cake just wont be as thick. You will need to really watch it toward the end of the baking time so that it does not over bake. It may be done a little sooner. Cut the Butter and Chocolate into pieces and place them both in a heat-proof bowl. Place in the microwave to melt for 20 seconds. Stir and repeat until the mixture is smooth. It should take 2-3 increments. Let this mixture rest for 2-3 minutes. (Alternatively, the butter and chocolate can be melted together in a double boiler.)
Add to the Butter and Chocolate mixture: the Sugar, Espresso Powder, Vanilla Extract, Orange Liqueur and mix together.
Whisk the 4 Eggs and then add them to the mixture. When the eggs are fully incorporated add: the Cocoa Powder, Salt, and Baking Powder.
Pour the batter into the prepared pan, and spread so that it is evenly distributed.
To the preheated oven, place a baking sheet on the very bottom rack and fill it with 2” or so of boiling water. This will create a moist baking environment for the cake. (*Please do not skip this step.)
Immediately after preparing the oven, place the cake on the center rack. Bake for 30-35 minutes, until the edges are set, and a toothpick inserted comes out clean. (The toothpick can have some crumbs on it, but not anything like a wet batter. This is one cake that should not be “over baked”, so check it earlier rather than later.)
Remove the cake from the oven and let it rest for 10-15 minutes. Afterward, run a sharp knife along the inside of the pan to loosen the edges of the cake, then invert the cake onto a serving platter or cake stand. COOL COMPLETELY before adding the Ganache or any toppings. (Usually 2 hours or so. Alternatively it can be placed in the refrigerator for an hour. )