Steam sweet potato to soft for about 20 minutes. Remove skin and mash sweet potato with a fork. Then blend with cream cheese and butter to smooth.
Combine egg yolk, milk, whipping cream, and golden syrup in another bowl, stir well.
Pour egg yolk mixture into step one and blend to a smooth dough. Then scope dough into piping bag and pipe into 6 or 7 mini cupcake liners evenly. Sprinkle some black sesame seeds on top and bake in preheated oven at 170 deg C for about 30-35 minutes.
Cake can be served warm or chilled.(I prefer to serve after chilled)