Add one scoop of ice to fill a cocktail shaker halfway then pour in half of the coffee concentrate (12 ounces) and half of the condensed milk. Shake vigorously to combine then pour evenly between two of the glasses filled with ice.
Repeat step two with the remaining coffee concentrate and condensed milk. Pour over remaining two glasses and serve immediately.
Notes
If you don't have a cocktail shaker pour the ingredients in a large pitcher and mix well before serving over ice.