Preheat the oven to 350 °F. Grease a cake pan and line the bottom with parchment paper.
In a large mixing bowl, sift together one and three-quarters of a cup of Bisquick, one cup of granulated sugar, and three-quarters of a cup of cocoa powder.
Mix one teaspoon of baking powder with one tablespoon of vinegar in a small bowl and set aside.
In a separate bowl, using an electric mixer, combine one and three-quarters of a cup of milk, two and one-half tablespoons of vegetable oil, one teaspoon of vanilla extract, and the baking soda mixed with vinegar.
Add the wet ingredients to the dry ingredients and continue mixing. Do not over-mix.
Pour the batter into the prepared baking pan and bake for forty minutes, or until a toothpick inserted into the middle comes out clean.
Transfer the cake to a wire rack and let cool before dusting with the confectioners’ sugar.
Serve and enjoy.