In a saucepan, heat coffee concentrate and 2 ounces of milk until steaming. Do not boil. Simultaneously, add 2 ounces cold milk to a second saucepan. Whisk milk while heating, and again, do not boil. Once you have enough foam, remove from heat. Pour coffee and milk mixture into a mug, top with foam, and serve.
In the microwave, heat coffee concentrate and 4 ounces of milk until steaming. Do not boil. If you'd like, use a hand frother to create foam.
In a milk frother, froth coffee concentrate and 4 ounces of milk. Pour coffee and milk mixture into a mug, top with foam, and serve.