Grind the coffee beans coarsely, similar to raw sugar.
Combine the grounds and 10 ounces filtered water in a clean jar; stir to fully wet the coffee.
Cover and steep at room temperature for 12–18 hours, until the concentrate tastes smooth and low in acidity (16 hours is a reliable midpoint).
Strain through a fine-mesh sieve lined with a paper filter or clean cloth; let drip without squeezing, then discard the grounds.
Filter once more through a fresh paper filter for clarity, if needed.
Chill the filtered concentrate until very cold, 1–2 hours, until it feels thoroughly chilled to the touch.
Dilute the cold concentrate 1:1 with 8 ounces filtered, chilled water to make 16 ounces ready-to-drink cold brew.
Pour the cold brew into a 1-pint (16-ounce) cream whipper rated for cold liquids, leaving just a little headspace; seal tightly.
Charge with 1 nitrogen (N2) cartridge, shake vigorously for 20–30 seconds, then add a second N2 cartridge and shake again for 20–30 seconds.
Rest the canister 30 seconds, then invert and dispense into a chilled glass at a slight angle; straighten the glass near the end to build a thick, cascading head.
Serve immediately while the foam settles into a creamy cap over the coffee.