To a small or medium saucepan add the grape juice, strawberries, and granulated sugar and bring to a simmer over medium heat.
2/3 cup strawberries, 1/4 cup white grape juice, 3 tbsp granulated sugar
Allow the mixture to simmer for about 8 minutes, making sure to mash the strawberries from time to time to really allow them to infuse.
Transfer to a tall measuring cup and blend using an emulsion blender. You can also blend this with a regular blender. Chill for later.
For the strawberry frappuccino
Add the milk, strawberry sauce minus two tablespoons, xanthan gum, and ice to a high-speed blender, and blend well.
1 cup ice, 2/3 cup milk, 1/8 tsp xanthan gum
To a tall glass add the 2 tablespoons of strawberry sauce that you set aside and pour the blendeds strawberry frappuccino over that. Top with whipped cream and enjoy!