Preheat oven to 170°C for a standard loaf tin, or 160-165°C for cast iron.

Grease your loaf tin slightly with some butter, then line it with parchment paper.

In a small bowl, whisk together cocoa powder, boiling water or espresso, and espresso powder until smooth.

In a bowl, beat together softened butter, neutral oil, sugars, vanilla extract, and espresso powder until light and fluffy.

Add eggs one at a time, beating well after each addition.

Mix the milk with sour cream, and separately whisk the dry ingredients.

Alternate adding the dry ingredients and wet ingredients in three parts, mixing until just combined.

Remove about ⅓ of the vanilla batter and fold in the cooled chocolate paste.

Layer the batters in the loaf tin to create a marble effect.

Bake for 60 minutes for a standard loaf tin or 70-75 minutes for a cast iron pan.

While the cake is baking, make the coffee cardamom syrup by simmering coffee, sugar, crushed cardamom pods, and cardamom powder.

Poke holes in the cake and brush the coffee cardamom syrup over it while still hot.

Let the cake cool in the tin for 15 minutes before lifting it out.

Store in an airtight container or cling film at room temperature for up to 5 days.

Chop the dark chocolate in random size pieces. Pour the cream into a small saucepan and place over medium heat. Bring the cream to a gentle simmer. Don't let it boil. As soon as it's simmering, remove from heat and pout over the chopped chocolate. Let it sit for 1 minute. Using immersion blender (for the smoothest texture) or with a whisk or silicone spatula, start stirring gently until it is glossy and everything is melted and emulsified.

Let it cool at room temperature for 30-45 minutes, stirring occasionally. As it cools, it will thicken from a pourable liquid to a thick, spoonable consistency.

Spoon a generous dollop of ganache and scrape it on top of the slice and sprinkle some flaky salt of course.