Note- One 3 ounce box of jello will do two cans of pineapple rings.
Drain the pineapple slices very well.
Mix the cup boiling water with the jello and stir until the jello is dissolved. Add the cup of cold water.
If you are adding mandarin oranges or cherries to the center of the pineapple do this now. Add enough to fill it to the top, I packed them in. Pour over the jello.
Place the cans into the fridge. Let chill for 6-hour or longer. I did overnight.
To remove the pineapple and jello from the cans. Flip the can over onto a plate and use a can opener to open the end. Push the pineapple and jello out, push it out toward the end of the can that has less of a lip on it.