Preheat oven to 300°F (150°C). Line a rimmed baking sheet with parchment paper.
Spread 1 cup granulated sugar evenly across the sheet. Bake, stirring every 15 minutes, until the sugar turns a pale yellow and smells slightly caramelized, about 60 minutes. Remove from oven and let cool.
Transfer cooled toasted sugar to a blender or food processor. Process until very fine, like powdered sugar.
In a large mixing bowl, whisk together the powdered toasted sugar, 1 cup Dutch-process cocoa powder, 2 cups powdered milk, 2 tablespoons cornstarch, and ½ teaspoon salt until well combined.
Stir in ½ cup malted milk powder, if using, and 1 teaspoon vanilla powder, if using.
Transfer to an airtight container. Store in a cool, dry place for up to 6 months.
Add 3 ½ tablespoons (28 grams) of the cocoa mix to a heat-safe cup. Pour 8 ounces hot water over top and stir until dissolved.
