Make some coffee. You'll need about a cup. Save a dish and brew it directly into a mason jar.
Add 1/3 cup powdered milk to your coffee in a quart-sized mason jar.
Put a lid on the mason jar and shake it up for about a minute. You'll want to use a canning lid, not a storage lid, or it will leak. Hold the jar with a towel or pot holders so you don't burn your hands.
Transfer to a mug, and enjoy! Or, just drink it straight out of the mason jar, if you want to save another dish.
Note: I also make mason jar lattes in a similar fashion with real milk, instead of powdered. Just put about 1/2 cup milk in the jar, heat it in the microwave, shake it, then pour it over 1/2 cup of extra-strong coffee. It doesn't foam up quite as much as the powdered milk, but it's still impressive for not using any specialized, coffee-shop machines. No pics of that, though, since I have no milk today.