1. Preheat oven to 325º. Spray an 8-inch square glass baking dish lightly with non-stick cooking spray.
2. For the Fudge Sauce: In a 2 cup glass measuring cup with a spout combine hot coffee, brown sugar, ¼ cup white granulated sugar and 1/3 cup cocoa powder. Stir until well combined and everything is dissolved; set aside.
3. For the Cake: Melt butter and chocolate chips together in the top of a double boiler, or in a small glass bowl set over a small pot of slow simmering water. When melted add 1/3 cup cocoa powder and stir until smooth; remove from heat and set aside to cool slightly.
4. In a small bowl combine flour, baking powder and salt; stir until well incorporated and set aside.
5. In a medium bowl whisk together ½ cup white granulated sugar with the vanilla, milk and egg yolk. Add the melted chocolate/butter mixture and whisk until well combined. Add the flour mixture and whisk until flour is incorporated, do not over mix at this point.
6. Spread the batter evenly into the prepared baking pan. Do one last stir of the fudge sauce to make sure everything is evenly incorporated.
7. Now here’s a strange step, but none the less it is the key to the Molten Fudge; pour the fudge sauce evenly and gently over the entire pan of batter.
8. Bake in the center of the oven for approximately 45 minutes. It is important not to over bake it. It will not really set in the center, but the sides of the top cake layer will pull away from the sides of the baking dish and the fudge sauce will be bubbly.
9. Place the baking dish on a wire rack to cool for about 25-30 minutes. It is best served warm at this stage with your favorite vanilla ice cream. You may also reheat leftover Molten Fudge Cake covered in the microwave.