Spray your slow cooker HEAVILY with nonstick spray or rub down with butter or oil.
Add the melted butter to the bottom of the slow cooker and sprinkle over the brown sugar. Mix lightly with a spoon and spread out evenly over the bottom of your slow cooker.
Lay down the pineapple rings on top of the brown sugar mixture. My slow cooker fits 6 perfectly. Add a cherry in the middle of each pineapple.
In a medium sized bowl add the cake mix, 1 cup of pineapple juice (if you don't have enough pineapple juice from the can, add water), eggs, oil and vanilla. Mix with a spoon until combined, do not overmix or try to remove the lumps.
Pour the batter over the pineapple in the slow cooker.
Place the lid on the slow cooker and cook on HIGH for 2 hours. If your slow cooker cooks hot, it may be a little less time. You know your cake is done when the cake is set in the center.
Remove the insert to a cooling rack when the cake is done. Let cool for about 20 minutes before attempting to turn over onto a platter or cutting board.
Flipping the cake on to a platter or cutting board works best with two people if possible.
Video
Notes
Put any remaining cake in an airtight container and store it on the kitchen counter for up to 3 days. If it takes longer than to eat, you can place it in the fridge for an extra couple of days.
Often crushed pineapple (or pineapple tidbits) are used instead of pineapple rings.
Put any remaining cake in an airtight container and store it on the kitchen counter for up to 2 days. If it takes longer than to eat, you can place it in the fridge for an extra couple of days.