Preheat your oven to 310°F (155°C), line an 8-inch springform pan with parchment paper, and lightly grease it with butter.
In a large bowl, sift together the flour, cocoa powder, baking powder, sugar, and salt until everything looks nice and blended.
Add the eggs, softened butter, vegetable oil, milk, and vanilla flavoring to the dry ingredients, then mix on low speed for 2 to 3 minutes until the batter is smooth and even.
Pour the batter into the pan, give it a couple of taps on the counter to knock out air bubbles, and bake for 60 to 70 minutes until a toothpick comes out clean.
Let the cake cool in the pan for 10 minutes, then carefully move it to a wire rack and wrap it in plastic once it’s fully cool; chill in the fridge for at least 1 hour.
Beat the mascarpone and powdered sugar in a small bowl until creamy, whip the heavy cream separately to soft peaks, then gently fold the whipped cream into the mascarpone mixture.
Slice the dome off the top of the cake to level it out, then cut the cake in half horizontally and spread the cream filling on the bottom half; place the top half back on.
Heat the cream for the ganache until it’s just starting to steam (not boiling), pour it over the chopped chocolate, wait a minute, then stir until smooth and glossy.
Pour the ganache over the top of the cake and use a spatula or spoon to spread it gently; you can coat the sides too if you’re feeling fancy.