Always with milk. I don't really have hot chocolate without milk. In fact it's the same with instant oatmeal
I just microwave the milk, then pour it into a cup with the powder. I use a fork to stir it and drop a candy cane in it. Marshmallow, too. Three small ones. Occasionally I'll use actual cream or half-and-half and cocoa powder and just a pinch of sugar... ohhhh. Grandma drops caramel in hers.
Now I want hot chocolate...