In a medium saucepan, combine the fresh cranberries, sugar, and water. Bring this mixture to a boil over medium heat. Cook for about 10 minutes, or until the cranberries burst and the mixture thickens slightly. Remove from heat and let it cool.
Once the cranberry mixture has cooled, whisk in the raspberry jello powder until fully dissolved.
In a large mixing bowl, combine the chopped walnuts and mini marshmallows.
Pour the cooled cranberry jello mixture over the nut and marshmallow mixture and stir until combined.
Gently fold in the sour cream until well mixed.
Transfer the combined mixture into a 9x13 inch glass dish, spreading it evenly.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or until set.
Once set, slice into squares to serve and enjoy!