Add 1 cup coarsely ground coffee to a clean large jar or pitcher. Pour 4 cups cold filtered water over the grounds, making sure all grounds are saturated. Stir gently with a spoon to ensure even wetting.

Steep

Cover the jar or pitcher with a lid or plastic wrap. Let the coffee steep at room temperature or in the refrigerator for 12 to 18 hours depending on desired strength (12 hours for lighter, 18 hours for stronger concentrate).

Strain

After steeping, strain the mixture through a fine-mesh sieve lined with cheesecloth or a coffee filter into a clean container. If needed, strain a second time to remove fine sediment. This yields a cold brew concentrate (about 3 to 3.5 cups).

Store

Cover the concentrate and refrigerate. It will keep well for up to 1 week chilled.

To Serve

Prepare glass

Fill a serving glass with 1 cup of ice cubes.

Dilute concentrate

Pour 1/2 to 1 cup cold brew concentrate over the ice, then add 1/2 to 1 cup cold water or milk to taste. Typical ratio is 1 part concentrate to 1 part water/milk; adjust based on strength preference.

Sweeten and finish

If you like your iced coffee sweetened, stir in 1–2 teaspoons simple syrup (or other sweetener) while the drink is cold so it blends easily. For a creamier drink, add 1–2 tablespoons cold cream or half-and-half and stir gently.

Serve

Taste and adjust — add more water/milk to loosen, more concentrate to strengthen, or more sweetener/cream to preference. Serve immediately with a straw or stirrer.

Cleanup

Dispose of used coffee grounds (compost if possible). Rinse the sieve, jar, and any utensils with warm water and mild detergent.