Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan, or line it with parchment paper for easy removal.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, salt, and cornstarch until evenly combined. Set aside.

In a heatproof bowl or using a double boiler, melt the 4 oz of unsweetened baking chocolate. Stir occasionally to ensure it melts evenly and doesn’t burn. Once melted, set aside to cool slightly.

In a separate bowl, beat the eggs using a hand mixer or stand mixer until light and fluffy. Add the evaporated milk, vegetable oil, vanilla extract, and the cooled melted chocolate. Mix until smooth.

Gradually add the dry ingredients to the wet mixture in two parts. Start mixing on low speed to avoid flour spilling, and increase to medium speed as the batter comes together. Mix until just combined.

With the mixer on low, slowly pour in the 1 cup of hot water. The batter will become thin, but that’s normal and necessary for a moist cake.

Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 10 minutes, then remove from the pan and place on a cooling rack to cool completely.

While the cake cools, make the ganache. In a saucepan, heat the heavy cream and whipping cream over medium heat until it just begins to simmer (do not let it boil). Once simmering, remove the pan from the heat and add the 8 oz of Swiss chocolate, stirring until smooth. Optionally, add the vanilla extract for enhanced flavor. Let the ganache cool slightly to thicken.

Once the cake has completely cooled, pour the Swiss chocolate ganache over the top, spreading it gently with a spatula to cover the entire surface. If you prefer, you can also spread a thin layer of ganache on the sides of the cake. Allow the ganache to set for 30 minutes before serving, giving it time to firm up.