Preheat the oven to 350°F (175°C). Grease and flour a baking pan.

In a mixing bowl, combine the flour, sugar, cocoa powder, baking soda, and salt.

In another bowl, mix the boiling water, vegetable oil, vanilla extract, espresso powder, and vinegar.

Pour the wet ingredients into the dry ingredients and whisk until smooth.

Pour the batter into the prepared baking pan.

Bake in the preheated oven for 30 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.