Heat oven according to the directions on the back of the box. DO NOT GREASE BOTTOM OF PAN.
Beat cake mix, water, butter, vanilla and eggs in large bowl on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
Melt 1/3 cup butter (or less, I use 2-3 Tbls) in an ungreased baking pan (I use an 8” square glass baking dish). Scatter on 1/2 cup (or less) brown sugar. Arrange canned pineapple slices over the sugar mix. Pour cake batter over the pineapple and bake.
Bake according to directions on the back of the box (based on altitude and size of pan you are using) adding 4 to 5 extra minutes baking time (due to the pineapple mixture) or until toothpick inserted in center comes out clean.
Run a knife around the edges to loosen and cool completely. Turn upside-down onto serving platter so the pineapple is on top.
Serve warm or cold topped with whipped cream or nondairy whipped topping, if desired. Enjoy!
Do not overbeat the mix. If you do, it will rise in the center, which can cause it to crack when you flip it over.