Pour the milk into a heavy-bottomed saucepan. Heat on medium-low until steaming. Do not allow it to boil.
Remove pan from heat. Add the chopped chocolate all at once.
Let sit 30–45 seconds, then whisk slowly until smooth and glossy. At this point it should already look noticeably thick.
Return the saucepan to very low heat. Whisk continuously for 4-6 minutes.You are looking for spoon-coating thickness with a slow, ribbon-like pour and no bubbles (bubbles=too hot). Add the salt and sugar. Remove from heat once it feels luxuriously dense.