In a medium sauce pot, combine the milk, cocoa powder, and brown sugar. Whisk these ingredients together thoroughly to create an even mixture without lumps.

Place the pot over medium heat. Whisk the mixture frequently as it heats up until it begins to steam and tiny bubbles appear around the edges, being careful not to let it boil.

Reduce the heat to low and stir in the semi-sweet chocolate chips. Continue stirring until the chocolate has completely melted and the mixture is smooth and creamy.

Remove the pot from heat. Stir in the vanilla extract and a generous pinch of sea salt to enhance the flavors. Serve immediately, and optionally top with whipped cream or marshmallows.