Preheat oven to 350°F. Grease an 8x8-inch baking pan with shortening and flour (or baking spray).

In the prepared pan, whisk together flour, cocoa powder, sugar, baking soda, and salt.

Make three wells in the dry mix. Add the vanilla extract and white vinegar into two smaller wells, and the vegetable oil into one larger well.

Pour the water over all the ingredients and whisk everything together until well combined. Use a spoon or spatula to ensure all corners of the pan are mixed.

Bake for 40 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.

Once cooled, sprinkle with powdered sugar or top with the optional buttercream frosting.

To make the frosting, place chocolate chips in a microwave-safe bowl. Microwave for 30 seconds at a time, stirring between intervals, until the chips are completely melted and smooth. Let cool completely to room temperature.

While the chocolate chips are cooling, place room temperature butter into a medium mixing bowl. Beat with an electric mixer on medium speed until light and fluffy.

Add 0.5 cup of powdered sugar and beat until smooth. Add the remaining powdered sugar, scraping the sides of the bowl with a spatula. Continue beating for about one minute until all the powdered sugar is incorporated.

Add the cooled melted chocolate and vanilla extract. Beat for 2 minutes until the frosting is light, fluffy, and has a smooth texture.

Frost the cooled wacky cake and enjoy!