In a large, heavy saucepan mix sweetened condensed milk, milk, cream and instant coffee crystals. Cook and stir over medium heat until the coffee crystals are dissolved.
In a heat-resistant bowl, beat the cocoa into the egg yolk. Gradually add the hot milk mixture to the cocoa mixture while whisking. Mix in about 2 cups of the hot milk mixure. Then mix the cocoa mixture with the remaining milk mixture in the large saucepan.
Bring to a boil, stirring constantly. Then cook 2 minutes more. At this point, you have decadent hot chocolate.
Remove from heat and let cool to lukewarm. Add the remaining ingredients and mix thoroughly.
Transfer to a bottle or jar and chill in the refrigerator. Shake well before serving.