Add instant coffee, cocoa powder, sugar, and hot water into a bowl.
Whisk continuously for 3–5 minutes until thick, glossy, and airy.
Add hazelnut syrup into the whipped mixture.
Whisk gently for 20 seconds to combine evenly.
Fill two glasses with ice cubes.
Pour 150 ml cold oat milk into each glass.
Spoon whipped chocolate hazelnut coffee generously on top.
Stir before sipping, or admire the foam like a rational adult.