Preheat the oven to 375°F. Lightly grease a 8" cake pan and line the bottom of the pan with a parchment paper.
In a large mixing bowl, sift flour, cocoa, baking soda and sugar.
In a small bowl, combine espresso powder and warm almond milk. Stir in oil and vanilla and whisk till combined.
Add the wet ingredients to dry ingredients and whisk until well combined. Quickly stir in the vinegar.
Pour the batter into the prepared pan and bake for 30~35 minutes or until the cake tester inserted into the center of the cake comes out clean.
Let cool for 10 minutes in the pan before turning it out onto a wire rack to cool completely.