In a medium microwave safe bowl, combine sugar, cocoa powder, and cornstarch.

Incorporate milk a little at a time into the dry ingredients, ensuring lumps are worked out.

Use a spatula to press against the sides of the bowl to mash out lumps.

Microwave the mixture for 3 minutes on high.

Stir well with a spatula, scraping down the sides of the bowl.

Microwave for 1 minute.

Stir again, scraping down the sides of the bowl and working out any remaining lumps.

Repeat the 1-minute microwaving and stirring process until a thick, shiny, pudding-like consistency is achieved (about 3-4 minutes total).

Watch closely to prevent boiling over.

Once shiny and thick, stir in vanilla, peppermint, or coconut extract (if using) and salt.

Serve warm immediately.