Coffee Base:

In a quart jar, stir together the water, coffee, brown sugar, and cinnamon.
Cover and refrigerate overnight.
Assembly:

Pour the coffee base through a fine-mesh sieve or strainer into a medium bowl, then strain it back into the jar for easy storage.
For each drink: Fill a tall glass halfway with ice. Pour in the coffee until the glass is about three-quarters full.
Add milk or half-and-half to taste.
Die of happiness.