Add cocoa powder, sugar, vanilla, salt and 2 tbsp half & half (or milk) to a microwave safe cup. Whisk vigorously until the mixture becomes smooth.
Microwave for 20 seconds and whisk again until smooth. Pour a small amount of milk in (about 1/4 cup) and whisk till smooth. Pour the remainder of the milk and whisk. Add ice, whipped cream and sprinkles if desired.