Add the instant coffee, sugar, and hot water to a small bowl. Whisk with a milk frother or electric mixer until thick and glossy, about 3 minutes. Whisking by hand takes 8-10 minutes.
Pour the milk into a glass. For an iced latte, add ice and use cold milk. For a hot latte, use warm milk.
Spoon the whipped coffee over the milk. Stir before drinking, or mix in half of the foam and leave the rest on top. Serve immediately.