Prepare the Cake:

• Preheat your oven to 350°F (175°C). Grease and flour an 8-inch (20cm) round baking pan.
• In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
• Add the egg, milk, vegetable oil, and vanilla extract to the dry ingredients. Mix until smooth and well combined.
• Carefully stir in the boiling water until the batter is well combined; it will be thin.
• Pour the batter into the prepared pan.
• 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 before transferring it to a wire rack to cool completely.

Prepare the Chocolate Ganache:

• In a small saucepan, heat the heavy cream over medium heat until it begins to simmer.
• Place the chopped semi-sweet chocolate in a heatproof bowl.
• Pour the hot cream over the chocolate and let it sit for 2-3 minutes.
• Stir the mixture until smooth and glossy.
• Allow the ganache to cool slightly until it thickens to a spreadable consistency.

Assemble the Cake:

• Once the cake has cooled completely, place it on a serving plate.
• Pour the ganache over the top, allowing it to drip down the sides.
• Let the ganache set before slicing and serving.