In a small bowl, toss the berries with the granulated sugar. Mash everything together with a fork. Set aside, allowing the berries to macerate until juicy, about 20 minutes.

Add the macerated berries to a blender or the bowl of a food processor and purée until smooth. If necessary, add 1-2 tablespoons of water to get the blades moving.

Pass purée through a fine mesh strainer to remove the seeds.

In a medium saucepan, warm the milk over low heat.

Add the white chocolate, stirring gently until completely melted.

Add the blueberry purée and sea salt, stirring occasionally until warmed through.

Pour into mugs. Garnish with homemade ghost marshmallows. Serve immediately.