Add hot water to the instant coffee, and stir until dissolved. Then add the condensed milk, salt and sugar to taste. Stir everything together and leave to cool down.
If you prefer more coffee, you can always add more instant coffee depending on how strong you like it. Serve over ice with equal parts milk and coffee concentrate. I’m a bit lactose intolerant so I like using soy milk, which tastes just fine (although pretty sure it’ll work with anything else!)