Credit to Alton Brown for the recipe, this stuff is tops!
2 cups powdered sugar
1 cup cocoa powder (Dutch process is preferred)
2 1/2 cups powdered milk
1 teaspoon salt
2 teaspoons cornstarch
1 pinch of cayenne pepper for a kick. More if you have high tolerance.
Combine everything in a ziploc bag, shake well to mix.
Portioning is 1/2 cup of mix to 1/2 cup of boiling water. This stuff is strong in flavor though, and I’ve found that you can use a little less mix and get away with it.