In a bowl, sift together the flour, cornstarch, and cocoa powder. Place the chocolate and milk in a separate, microwaveable bowl, and melt the chocolate in the microwave. This should take around 60 seconds on high power, or you could do this in a water bath as well. Then, add the oil and egg yolks to the dry ingredients, give it a quick mix until it comes together into a paste, then add in the chocolate milk. Stir and mix to combine it all, until a smooth batter forms.

Heat the oven to 160°C. Line a deep 7-inch cake tin with baking paper, and prepare a wider, shallower baking tray (I used a 10-inch). The reason we’re doing this is because the cake will be baked in a water bath, so we’ll be filling the wider tray with hot water, while the cake tin sits within it. So, with that in mind, this is a good time to boil some water too, approximately 500ml should do it.

Place the egg whites, salt, and lemon juice in a stand mixer fitted with a whisk attachment, and whisk it on high. After 1 minute of mixing, and the egg whites turn foamy, add in the sugar, and whisk it for another 2-3 minutes, until stiff peaks form.

Take about a quarter of the meringue, and mix it through with the chocolate batter. This will lighten the latter. Then, in 2-3 inclusions, gently fold the rest of the meringue into the batter, making sure there are no streaks of meringue remaining, but also being careful not to overmix and deflate the batter.

Scoop half of the batter into the lined cake tin, and smooth out the top with a spoon or spatula. Then, with a microplane or grater, grate the 40g of chocolate onto the batter, making sure to get an even coating throughout. (This step is totally optional, but it creates a thin layer of melted chocolate within the cake, which I think is sublime. And in fact, you can even try doing a double layer of chocolate, so placing 1/3 of the batter instead of the 1/2, and repeating the process once more.) When done, place the rest of the batter on top of the grated chocolate and first batter layer, then smooth out the top, and give it an even sprinkling of gochugaru.

Place the batter-filled cake tin within the larger tray, and fill the larger tray with water, until at least 1-inch of the cake tin is submerged. Then, pop this whole set-up into the oven (careful; don’t spill it!) and bake for 50-60 minutes, until a cake tester poked through the middle of the cake comes out clean.

When the cake is done, take it out of the oven, and remove the cake tin from the water bath, and set it on a wire rack. After letting it cool for at least 15 minutes, remove the cake from the cake tin, tear away the baking paper, and leave it for a further 10 minutes, until it cools to room temperature. Then, slice the cake up into large slabs (or thin wedges if you’re tryna control yourself from eating too much), and eat!