Dissolve the Gelatin: In a large heat-proof mixing bowl, pour your 2 cups of boiling water over the Jello powder. Whisk continuously for about 2 minutes until the sugar and gelatin are completely dissolved and no granules remain at the bottom.
Temper with Cold Water: Stir in the 1 cup of cold water. This helps lower the temperature of the liquid so the fruit doesn't "cook" when you add it. Let it sit for about 5 minutes to cool slightly.
Incorporate the Fruit: Gently fold in the whole berry cranberry sauce and the drained crushed pineapple. Use a spatula to break up the cranberry sauce so it distributes evenly throughout the mixture.
Add the Crunch: If you are using chopped pecans, stir them in now. The nutty flavor provides a beautiful contrast to the soft gelatin.
The Setting Phase: Pour the mixture into a 9x13 inch glass dish or a decorative Jello mold. Cover it tightly with plastic wrap and refrigerate for at least 4 hours, though letting it set overnight is the best way to ensure it holds its shape perfectly.
Serve and Garnish: Once firm, slice into squares or unmold. Top each serving with a dollop of fresh whipped cream right before it hits the table.