Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.
In a separate bowl, mix together the brewed coffee, vegetable oil, vanilla extract, and apple cider vinegar.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.