Pour the boiling water into a mixing bowl and add the gelatin powder. Stir continuously until completely dissolved.
Add the cold water to the bowl and mix well.
Stir in collagen peptides, lemon or lime juice, and a pinch of salt if desired. Whisk until smooth.
Pour the mixture into small serving cups or containers.
Place the cups in the refrigerator for 2 to 4 hours until the gelatin sets firmly.
Enjoy chilled as a light dessert or snack.
