In a saucepan, heat coffee concentrate until steaming. Do not boil.
Simultaneously, fill another saucepan with 2 ounces cold milk. Whisk the milk while heating, and do not boil. Once you have enough foam, remove from heat. Pour coffee concentrate into a mug, top with foam, and serve.
In a microwave, heat coffee concentrate until steaming. Do not boil. Then heat 2 ounces cold milk. (Again, do not boil.) Use a whisk or a hand frother to foam the milk. Top the coffee concentrate with foam, and serve.
In a milk frother, add 2 ounces cold milk. Heat the coffee concentrate until steaming. Do not boil. Top with foam and serve.
Warm the milk for frothing.