A good recipe for homemade iced coffee uses the cold-brew method to prepare the coffee and then dilutes the extra-strong mixture with milk or cream over ice. For Viennese coffee, add sweetened condensed milk to the coffee, and dilute with water.
Prepare the cold-brew coffee by placing 1 pound of dark-roast coffee in a large container and adding 8 quarts of water. Stir to mix the coffee and water, cover, and allow the mixture to sit at room temperature for eight to 24 hours.
Place two layers of cheesecloth in a strainer, and hold the strainer over another large container. Pour the coffee through the strainer to remove the grounds. Do not pour the grounds from the bottom of the first container into the strainer.
Store the prepared cold-brew coffee in the refrigerator. Keep a cover on the container to prevent it from absorbing odd flavors. The prepared coffee lasts up to five days with refrigeration.
For each serving of iced coffee, fill the glass with ice. Pour in enough coffee to fill the glass two-thirds full. Add milk to the glass to fill it. Add sugar or replace the milk with sweetened condensed milk if you want to sweeten the coffee. Stir the contents, and serve.