Mix 6 cups water and coffee in a 1/2-gallon jar (such as Ball(R)) until grounds are completely saturated. Steep for 24 hours at room temperature, stirring occasionally.
Transfer the coffee to the refrigerator and chill for 1 hour.
Place a small colander on top of a tall, lidded plastic container. Line colander with a 6-inch square of cheesecloth; fit a coffee filter on top.
Pour about 1 cup of the coffee into the colander until filter begins to clog. Lift the corners of the cheesecloth carefully; twist the cloth and filter to extract the liquid. Drain the remaining liquid 1 cup at a time, using a new coffee filter each time. Repeat the process with the grounds, filtering 1 cup at a time; squeeze out as much liquid as you can. Refrigerate the concentrate until ready to use.
Combine concentrate, 1% milk, and condensed milk in a 1/2-gallon jar.
Dissolve 3 tablespoons plus 1 teaspoon sugar and cocoa powder together in a bowl of hot tap water. Add to the coffee-milk mixture; cover the jar and shake well.
