In a medium saucepan, heat the milk and sweetener of your choice over medium-low heat until it just warms, whisking every 30 seconds or so. Don’t be tempted to turn up the heat--milk scorches easily!
In a separate small bowl, sift the cocoa and salt powder using a fine-mesh strainer. Once the milk is warm to the touch, remove about ¼ cup of milk and pour over the cocoa powder. Whisk well until the cocoa powder is fully incorporated and dissolved into the milk and then pour the cocoa mixture back into the milk whisking to combine.
In the same bowl that you whisked the cocoa powder, add the chocolate chunks or chips. Pour 1 cup of the warm milk over the chocolate and stir until the chocolate is completely melted. Whisk the melted chocolate back into the saucepan.
Continue to heat over medium-low heat just until the mixture is fully warmed--about 2-3 minutes. Taste and add more sweetener if desired, whisking to melt the sugar into the hot chocolate.
Turn off the heat and stir in vanilla extract.
Serve the hot chocolate with whipped cream or marshmallows.
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Notes
For the milk: Whole milk is best for a decadent result, but feel free to use 2% or 1% milk if that is what you have on hand. If using dairy-free milk, almond milk or canned coconut milk are good options.For the chocolate, use chopped-up chocolate bars or simply use chocolate chips. Dark chocolate, semi-sweet chocolate, or dairy-free chocolate are all great options. For the sweetener: It is important to remember that the type of chocolate you use, determines the amount of sugar you need to add. When using milk chocolate, start by adding only 2 tablespoons of sugar to the milk. For semi-sweet or sweetened dark chocolate, start with ¼ cup of sugar and increase to taste, if needed. If using bittersweet or unsweetened dark chocolate, you will likely need to use ⅓ to ½ cup of sugar to sweeten the hot chocolate. Storage: Leftover hot chocolate can be stored in an airtight container for up to 3 days in the refrigerator. Reheat as desired.