Place chips in a heatproof bowl (preferably with a spout), and set aside.
Combine milk and sweetened condensed milk in a small saucepan and heat over medium-low heat, whisking frequently. (The faster you whisk, the foamier the milk will be.)
When the milk mixture looks like it's about to boil, remove from heat and pour into bowl over the chips.
Let sit about 1 minute, then add salt and whisk until completely smooth.
Pour into a mug and enjoy.