Pour the sweetened condensed milk into the bottom of a glass. Use more or less sweetened condensed milk depending on how sweet you like your coffee.
Use a phin Vietnamese coffee filter (~6 ounces) or a French press to brew the coffee. If using a Vietnamese filter, remove the top screen and spread the coffee grounds evenly inside the filter. If your filter has a screw mechanism, screw down until the grounds are gently pressed, but not too tight.
Place the filter over the glass containing the condensed milk. Pour a little hot water (just enough to wet the coffee grounds) into the filter and let it sit for about 20 to 30 seconds. This allows the coffee to "bloom."
After the bloom, fill the filter with hot water. The coffee will slowly drip into the glass over the sweetened condensed milk. This process might take 4 to 5 minutes. Be patient and enjoy the aroma!
Once all the coffee has dripped through, stir well to mix the coffee with the sweetened condensed milk until it's smooth and creamy. Drink it hot, or if you prefer an iced version, fill another glass with ice cubes and pour the mixed coffee over the ice.