Cold foam is just milk and cream whipped cold until it holds its shape. The trick is keeping everything as cold as possible, from the jug to the spoon.
The recipe
Two parts nonfat milk, one part cream, a spoon of maple syrup and a small pinch of flaky salt. Whip it in a chilled jug for about thirty seconds, until it looks like melted ice cream.
Pouring it
Spoon it over the drink slowly so it sits on top instead of sinking. The foam should be thick enough to hold a straw for a second before it tips.