It was a trend that had a little burst of popularity. It’s a type of frappe that is popular in Korea. It’s made with instant coffee, sugar, and water. Whip that until it forms silky peaks. Take a tall glass with ice, add 8 oz of milk, top with the whipped coffee mixture.
When everything shut down and supply chains were temporarily disrupted, coffee shops were closed and fresh coffee beans were at a premium. Dalgona coffee is a fancy frappe made with cheap, shelf-stable ingredients (you could substituted the milk for nut milk or powdered).
It is good, and really easy to make. Matter of fact, I could use one right now.