Lightly grease an 8.1" square pan at least 2" deep. If your pan isn't 2" deep, us a 9" square pan.
Whisk together the dry ingredients. In a separate bowl, whisk together the vanilla, oil, eggs, water, and rum.
Pour the wet ingredients into the dry ingredients, stirring until thoroughly combined.
Spread the batter in the prepared pan. Let the cake rest on the counter for 15 minutes. While the cake is resting, preheat the oven to 350 degrees.
Bake the cake for 28 to 32 minutes, until a wooden pick inserted into the center comes out clean.
Remove the cake from the oven, and cool it in the pan. Serve warm or at room temperature. Store, covered with plastic wrap, at room temperature for several days.