Heat oven to 175 C / 350 F. Grease a 9-inch round cake pan and line the base with parchment paper.

Melt the chopped chocolate with 60 ml of the olive oil in the microwave in 20-second bursts, stirring between each, until smooth. Set aside to cool slightly.

Whisk the flour, cocoa powder, baking soda, baking powder, and salt together in a medium bowl.

In a large bowl, whisk the eggs, granulated sugar, and brown sugar for 2 minutes until pale and slightly thickened.

Whisk the remaining 120 ml olive oil, the melted chocolate mixture, buttermilk, and vanilla into the egg mixture until smooth.

Fold the dry ingredients into the wet ingredients in three additions, stopping as soon as no streaks of flour remain.

Pour the batter into the prepared pan and tap it firmly on the counter twice to release air bubbles.

Bake for 35 to 40 minutes, until a toothpick comes out with a few moist crumbs and the internal temp reads 200 F / 93 C. The center should spring back lightly when pressed, a clean toothpick means it's overbaked and will dry out.

Cool the cake in the pan for 15 minutes, then turn it out onto a wire rack.

Once fully cool, drizzle with a little extra olive oil and sprinkle with flaky sea salt before slicing.