Preheat your oven to 350°F (175°C) and get your loaf pan ready by greasing it and lining it with parchment paper. I like to lightly spray the parchment too, it makes lifting the cake out a total breeze.

Whisk the flour, baking powder, and salt thoroughly in a large mixing bowl to ensure uniform distribution. Give it a little shake or stir to break up clumps, this step ensures your cake rises evenly and stays light and tender.

In another bowl, crack in the eggs and whisk in the buttermilk, melted butter, vegetable oil, both sugars, and vanilla extract. Mix until smooth, but don’t overdo it, overmixing can make your cake a bit heavy instead of soft and fluffy.

Gently fold the wet ingredients into the dry with a spatula. Move slowly and fold in one direction while turning the bowl; this keeps the batter airy and ensures everything is nicely combined.

Take half of the batter and mix it with the cocoa powder and hot water. Stir gently until smooth, a few tiny lumps are totally fine and add to the cake’s character and richness.

Alternate spoonfuls of the vanilla and chocolate batters into the prepared loaf pan, creating a layered effect. Use a butter knife or skewer to swirl them together, creating a pretty marbled pattern. Swirl just a few times, you want defined chocolate ribbons, not a muddy mess.

Bake on the middle rack for about 55–65 minutes, checking around 55 minutes. Stick a toothpick in the middle—if it pulls out clean or with a couple of soft crumbs, you’re good to go.

Let the cake cool in the pan for about 10 minutes before lifting it out. Gently loosen the edges with the parchment, this makes transferring it to a wire rack smooth and keeps the top looking flawless.

For the ganache, heat the heavy cream just until it starts to simmer, then pour it over the chopped dark chocolate. Let it sit for a few minutes, then stir until silky and glossy. Sprinkle in a pinch of salt to boost the chocolate flavor. If it feels too runny, give it 10–15 minutes to thicken, it will spread perfectly without sliding off.

Spread the ganache over the cooled cake with a spatula. Slice generously and enjoy.