Heat oven to 350°F. Get out a 9x9" baking pan, and set it aside (there is no need to grease it).
In a large bowl, whisk together 1 1/2 cups all-purpose flour, 1 cup granulated sugar, 3 Tablespoons cocoa powder, 1 teaspoon baking powder, 1 teaspoon baking soda, and 1/2 teaspoon table salt.
Using the back of a spoon or a small measuring cup, make 3 indents into the flour mixture. Pour 3 Tablespoons canola oil, 1 Tablespoon white vinegar, and 1 teaspoon vanilla extract into each of the indents.
In a measuring cup, dissolve 1 teaspoon instant coffee powder (if using) into 1 cup lukewarm water. Pour this mixture over the mixture in the large bowl, and mix with a spatula until no dry bits remain.
Spread the batter into the baking pan and bake for 30 minutes, or until a toothpick comes out with just a few crumbs clinging to it.
Easy Chocolate Frosting (Optional)
Make the frosting just before the cake will be done, or immediately after taking it out. Add 1 Tablespoon butter (no need to soften), 1 1/2 cups powdered sugar, 1 Tablespoon cocoa powder, 1/2 teaspoon vanilla extract, 1 pinch salt, 1/4 teaspoon instant coffee powder , and 2 Tablespoons hot water to a medium bowl. Mix on low speed with a hand mixer, then when all of the powdered sugar has been incorporated, turn up to medium. Mix for about 1 minute, then spread onto the cake while it is still hot.
Cool the cake to room temperature before serving.
Notes
If you don't have any instant coffee but still want to add a hint of coffee flavor to your wacky cake, simply replace the warm water in the recipe with a cup of cooled coffee (leftover coffee from the morning will do just fine). This works for the frosting too.