place the instant coffee into a heat-safe pitcher (I just use my Pyrex measuring cup) and add the hot water, mixing until it's dissolved. Place the coffee in the fridge for 10 minutes to cool it down. (Note: make sure you're water isn't too hot (i.e. boiling) or it's possible the shock from super hot to very cold in the fridge could crack your vessel. You don't need very hot water for this recipe anyways, just hot enough to properly dissolve the instant coffee - tap hot should be fine)
For each glass (this recipe makes 2) mix 3 tbsp of condensed milk and 3 tbsp of whole milk with a spoon in the glass until fully mixed, then add ice, coffee, and vanilla extract. Stir the drink together with a spoon or straw to mix.