Cold-brewing involves steeping ground coffee in cold water. RBC NYC coffee bar (rbcnyc.com) uses the method here.
Slideshow: Coffee Drinks
In a bowl, stir the cold water into the coffee. Cover and let stand at room temperature for 24 hours; strain. (The concentrate can be refrigerated for up to 1 week.)
Pour condensed milk into a tall glass. Add 6 ounces of cold-brew concentrate and the milk. Stir well. Top with ice.