I have never tried butter coffee, if it is as you say it is a special part of the traditional culture of Nanyang, I trust it must taste good, plus the way you describe, it encourages me to want to try it, I will try to find out more about it, it intrigued me a lot, greetings.
If you want to try, double shoot espresso, 2 tsp condense milk and 15gr butter, Its really works for mood in the morning :D
Thanks for the recipe, copied, I'll share my experience later. Happy day, greetings