Preheat the oven to 350ºF. Spray a 9- x 9-inch inch baking pan with baking spray and set aside. If you'll be serving the cake out of the pan, line the bottom with parchment paper.
In a medium bowl, whisk the flour, sugar, cocoa powder, espresso powder, baking soda, and salt together.
Add the canola oil, vinegar, and vanilla, then pour the boiling water over it all and whisk until smooth.
Pour the cake into the prepared pan and bake for 28 to 30 minutes or until a cake tester inserted in the center of the cake comes out clean.
Allow to cool for 30 minutes. Dust the cake with powdered sugar, serve it from the pan, and enjoy!
Dark chocolate cocoa powder and espresso powder give this cake an intense chocolate flavor. Feel free to substitute regular cocoa powder and/or omit the espresso powder if you prefer.If you prefer to serve the cake out of the pan, allow it to cool for 15 minutes in the pan then turn it out onto a cooling rack. Transfer to a platter and dust with powdered sugar before serving.For a different presentation, make a half recipe in a 6-inch round cake pan lined with parchment paper sprayed with baking spray. Bake for 20 to 25 minutes.Want cupcakes instead? Try my one-bowl frosted chocolate cupcakes baked in a standard muffin pan.For a fast and easy single serving, bake a mug cake in the microwave instead!