Directions
Step 1
Let the yolks and whites come to room temperature. Position a rack in middle of the oven and heat to 325°F. Line a 10×13 pan with parchment paper but do not grease it. Sift flour and baking powder together; set aside.
Step 2
By hand or in a stand mixer, whisk the egg yolks and 1/2 cup sugar in a large bowl until pale and well combined, about 2 minutes. Whisk in olive oil, vanilla, and water, then fold in the dry ingredients.
Step 3
By hand or in a stand mixer, beat the egg whites, salt, cream of tartar, and the remaining 1/2 cup sugar until egg whites are foamy. Increase the speed to high and beat until the whites are thick and glossy, about 8 minutes. Gently fold the whites into egg yolk mixture in 3 or 4 batches.
Step 4
Transfer the batter to the pan and use an offset spatula to smooth the surface. Bake for about 25 minutes, rotating the pan after 12 minutes. When done, the cake will start to shrink from the sides of the pan, and the tip of a sharp knife will come out clean. Cool in the pan for 10 minutes, then invert onto a rack, peel off the parchment, and let cool completely (it can be made a day in advance, wrapped when cool, and left on a counter).
Step 5
Once the cake has cooled, trim any rough edges and cut into approximately 1 1/2-inch squares. Place the squares on a rimmed sheet pan in the freezer for 30 minutes—this will help prevent any crumbling and shorten the time it takes for the icing to set.
Step 6
While the cake is in the freezer, make the icing: Melt 6 ounces chocolate in the microwave on low power. When nearly melted, remove from the microwave and add the remaining 2 ounces of chocolate; stir until fully melted. Stir in the olive oil, then the vanilla; set aside.
Step 7
Mix the powdered sugar, cocoa, and espresso powder in a large bowl. Add 1 cup boiling water and stir until smooth. Fold in the melted chocolate mixture and stir again; it should be fluid but not too thin. If too thick, add more boiling water, one tablespoon at a time. Set aside until the cake is ready.
Step 8
Set up your counter assembly line–style for dipping. Line a rimmed sheet pan with parchment paper and place it to one side for the dipped cakes. Pour the coconut into a glass pie plate and place it next to the bowl of icing.
Step 9
Take half the cake squares from the freezer to the counter; leave the rest in the freezer until you finish the first batch. To dip, lower one cake square into the icing and use two forks to rotate it so that it’s completely covered in chocolate. Lift the cake out with a fork, tap the fork against the side of the bowl so any excess chocolate drips off, and place the cake square in the coconut. Use two clean forks or your fingers to cover it in coconut and transfer to the prepared sheet pan. Repeat with the rest of the squares. Note: If the icing gets too thick while you’re working, thin it with hot water, 1 tablespoon at a time.
Step 10
Let the cakes sit until the icing is set, about 30 minutes. They can be stored in an airtight container on the counter.