📖 Instructions

1. Preheat your oven to 325°F (160°C). Grease a 9-inch springform pan and line the bottom with parchment paper. This ensures easy release after baking.
2. In a double boiler or heatproof bowl set over simmering water, melt 6 ounces of the bittersweet chocolate and the butter, stirring occasionally until smooth. Remove from heat and let cool slightly. It's okay if the mixture isn't perfect; we're aiming for a melted, not burnt, situation here.
3. In a large mixing bowl, whisk together the granulated sugar, brown sugar, cocoa powder, flour, baking powder, baking soda, and salt. Make sure there are no clumps! Seriously, those little cocoa clumps are no fun.
4. In a separate bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla extract until well combined. Don't over-whisk; just make sure everything is incorporated.
5. Gradually add the wet ingredients to the dry ingredients, mixing on low speed until just combined. Be careful not to overmix; a few streaks of flour are fine at this stage. We're not trying to build gluten here.
6. Stir in the hot water until the batter is smooth and quite thin. Don't worry; this is normal! The batter will seem surprisingly liquid, but trust me, it'll bake up beautifully.
7. Pour the melted chocolate mixture into the batter and stir until evenly combined. Now, the batter should look rich and decadent.
8. Pour the batter into the prepared springform pan and bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out with a few moist crumbs attached. Every oven is different, so keep an eye on it!
9. Let the cake cool in the pan for 15 minutes before releasing it and transferring it to a wire rack to cool completely. Patience is key here; the cake needs time to set.
10. While the cake is cooling, prepare the ganache. In a heatproof bowl, combine the remaining 6 ounces of bittersweet chocolate and the heavy cream.
11. Microwave in 30-second intervals, stirring in between, until the chocolate is melted and the ganache is smooth. Alternatively, use the double boiler method. I personally think the microwave is easier, but do what makes you happy!
12. Let the ganache cool slightly, about 10 minutes, until it thickens to a pourable consistency. This is important; otherwise, it'll just run right off the cake!
13. Pour the ganache over the cooled cake, allowing it to drip down the sides. For an extra touch, sprinkle with sea salt flakes. Or don't; it's your cake!
14. Let the ganache set before serving. This usually takes about 30 minutes at room temperature or 15 minutes in the refrigerator. If you're impatient (like me), the fridge is your friend.