Combine the cake mix, flour, salt, and rainbow sprinkles in a large bowl.

Cut in the cold butter with a pastry cutter or two forks until coarse crumbs form.

Whisk the vanilla extract into the heavy cream. Create a well in the flour-butter mixture and pour the liquid ingredients into the well in two separate parts, mixing until a dough forms. **Note: You may not need the entire cup of cream.

Pour the dough out onto a lightly floured surface. Turn the dough a couple of times until it comes together—do not overmix. Form the dough into a 7-inch circle about ¾-inch high.

Cut the disk of dough into eight triangles using a sharp knife or bench scraper. Place the dough triangles onto a parchment-lined baking sheet and place the tray in the refrigerator for 30 minutes to 1 hour to chill.

Preheat the oven to 400°F. Brush the tops of the scones with heavy cream and bake them for 18-20 minutes until golden brown—cool the scones on a wire rack.

Whisk the powdered sugar and milk until a glaze forms. Drizzle the glaze over the cooled scones and sprinkle with additional rainbow sprinkles. Let the glaze set before serving.