- In a large mixing bowl, combine the mixed frozen fruit and mini marshmallows. 
- In a separate bowl, whisk together the whipped topping, sour cream, granulated sugar, and vanilla extract until smooth. 
- Gently fold the whipped topping mixture into the fruit and marshmallow mixture until well combined. 
- If using, fold in the chopped nuts for added texture. 
- Transfer the mixture into a 9x9-inch baking dish or a similar-sized container, spreading it evenly. 
- Cover and freeze for at least 4 hours or until firm. 
- Before serving, let the salad sit at room temperature for about 10 minutes to soften slightly for easier scooping.