Preheat oven to 325°F. Grease a 9-inch springform pan and line the bottom with a round of parchment paper.
In a heatproof measuring cup or small bowl, whisk together the cocoa powder and boiling water until smooth. Add the vanilla and stir until a thick, glossy paste forms. Set aside to cool slightly.
In a medium bowl, whisk together the almond flour, baking soda, and salt, breaking up any lumps. Set aside.
In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, beat the sugar, olive oil, and eggs on medium to medium-high speed until the mixture is pale, thickened, and slightly increased in volume, about 3 minutes, scraping down the bowl once or twice as needed.
Reduce the mixer speed to low and add the cocoa mixture, beating until fully combined and no streaks remain.
With the mixer on low, gradually add the almond flour mixture and mix just until combined and the batter is smooth.
Use a spatula to scrape the bottom and sides of the bowl to make sure everything is evenly incorporated.
Pour the batter into the prepared springform pan and smooth the top with a spatula. Bake for 40 to 45 minutes, or until the edges are set and the center is slightly domed and looks just a bit damp; a toothpick inserted near the edge should come out mostly clean, while the very center may have a few moist crumbs.
Transfer the pan to a wire rack and let the cake cool in the pan for 10 minutes.
Carefully unlatch the springform ring and remove the sides. Slide a thin spatula under the parchment to loosen, then transfer the cake directly to the rack to cool completely, 30 to 45 minutes.
Just before serving, dust the top lightly with powdered sugar, if desired. Slice with a sharp knife, wiping the blade between cuts for the cleanest slices, and serve.