In a large mixing bowl, beat the softened butter and sugar together until creamy. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.

In another bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, alternating with milk. Mix until just combined.

Preheat your oven to 350°F (175°C). Grease and line the bottom of the cake pan with parchment paper. Pour the batter into the prepared pan and smooth the top. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Once baked, remove the cake from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a wire rack to cool completely.

In a saucepan over medium heat, bring the heavy cream to a simmer. Remove from heat and add the chopped chocolate. Stir until the chocolate melts and the mixture is smooth. If desired, add butter for extra shine.

Once the cake has cooled completely, pour the chocolate ganache over the top, allowing it to drip down the sides. Let it set for about 15 minutes before slicing.