Pour the cold water into a medium-sized bowl and sprinkle the unflavored gelatin evenly over the top. Allow it to sit (bloom) for 5 minutes.
Pour the boiling water (or hot sugar-free liquid) over the bloomed gelatin and whisk continuously until the granules are completely dissolved.
Allow the mixture to cool down to warm room temperature. Note: Adding protein powder to boiling liquid will cause it to clump.
Once the liquid is warm (not hot), slowly whisk in the whey protein isolate. For best results, mix the protein with a small splash of cold water first to create a paste before adding to the gelatin.
If using sweetener or making the 'fluffy' variation, fold in the sweetener or whipped topping now.
Pour the mixture into individual serving containers or molds.
Refrigerate for at least 3 to 4 hours, or until the gelatin is firm and set.