In a small bowl, whisk 1 tablespoon 2% milk or whole milk with ½ teaspoon cornstarch until no clumps remain. Set aside
Make the Hot Chocolate:
In a 3-quart saucepan, add 2 tablespoons granulated white sugar, 1 to 2 tablespoons cocoa powder, 2 cups 2% milk or whole milk, and A pinch of salt. Bring to a boil, then reduce the heat and simmer the mixture for 5 minutes. Whisk frequently to ensure the cocoa powder melts into the milk. Taste and adjust, adding the additional cocoa powder if desired.Note: Lower the heat as needed to prevent the milk from burning.
Add 1 ounce 70% finely chopped dark chocolate (if using) and cornstarch slurry (if using) and bring to a boil. Whisk constantly for 2 minutes at a boil. Note: Cornstarch needs to boil for at least one minute to activate and thicken.
Taste the hot chocolate and adjust flavorings as needed. Not sweet enough? Stir in additional sugar. Not chocolatey enough? Stir in additional cocoa powder or chopped chocolate.Note: Keep in mind the marshmallows will add more sweetness to the hot chocolate. Salt really brings out the chocolate flavors, so if you feel the hot chocolate needs something extra, try adding another pinch.
Remove from the heat then stir in ¼ teaspoon vanilla extract. Divide hot chocolate amongst two mugs and top with marshmallows.
Notes
The cornstarch slurry is optional, but it helps thickens the hot chocolate. For a creamier hot chocolate, replace milk with half-and-half or heavy cream.For a flavored hot chocolate, replace the vanilla extract with any extract you like, such as almond, peppermint.Here are some of my favorite hot chocolate toppings: marshmallows, candy canes, whipped cream, and salted caramel.