Simmer the water and sugar for a bit over a heat source. Add the coffee in one batch and dissolve.
Alternatively, add the water and sugar to a large bowl and heat in a microwave at 1000 W for roughly 1 1/2 minutes until the mixture has reduced a bit. Mix together thoroughly, then add the coffee.
Warning: If cooking in a microwave, be sure to use a big bowl or else it will overflow.
Leave Step 1/2 to cool.
Add in the alcohol little by little, and mix thoroughly.
Store in a sterilized jar. I wet the bottle and microwave at 1000 W for 2 minutes.
The alcohol content of this drink is fairly low. If you like it stronger, increase the amount of alcohol to 150 ml from 120 ml.
This is the instant coffee that I use.
For the beverage in the main picture, I mixed 1 part milk to 1.5 parts Kahlua.
Memo: can be made by infusing 30 g coffee beans, 50 g rock sugar, and 1 cup of alcohol. After 2-3 weeks, strain to produce Kahlua.
However, this method always results in a high alcohol content.
Story Behind this Recipe
Liqueur made from coffee beans always has a very high alcohol content. And it doesn't taste like Kahlua. I live in a country where Kahlua isn't available in shops. I usually buy it in duty-free import shops. When I tried instant coffee, it tasted really similar to Kahlua, so I did a bit of experimenting.
In order to get this how I like it, I made it over 10 times. This time, I used 35 % Eau Du Vie (sweet brandy). I can't drink strong alcohol because of my age, so I only used 120 ml. If you use 150 ml it's quite strong -- I think probably the same as Kahlua. Probably.... the real stuff should be around 20%.