Adjust oven rack to middle position and preheat oven 350°F (175°F). Lightly spray a 9-inch round cake pan with cooking spray. Line bottom of pan with parchment paper, and set aside.
In a small bowl, whisk ¾ cup water and espresso powder until fully dissolved, about 30 seconds. Set aside.
In a large bowl, whisk granulated sugar, flour, cocoa, salt, baking powder, and baking soda. Add eggs, buttermilk, olive oil, vanilla, and reserved dissolved espresso powder. Stir until combined. Pour batter into prepared pan.
Bake until a wooden pick inserted into center of cake comes out with just a few moist crumbs, 40 to 45 minutes. Transfer cake to a wire rack and let it cool in the pan for 15 minutes. Using a butter knife or offset spatula, gently loosen edges of cake from pan. Invert cake onto wire rack and return cake right side up. Let cake cool to room temperature, about 1 hour. Transfer cake to a serving plate, carefully peeling off parchment paper. Drizzle with additional olive oil, dust with confectioners' sugar, and serve with vanilla ice cream, if using.
