Toast the black sesame seeds in a dry skillet over medium heat for 3-4 minutes until fragrant. Let them cool. Grind the toasted sesame seeds into a fine powder using a food processor or spice grinder. Mix the sesame powder with sugar, melted butter (or coconut oil), and water until it forms a smooth paste. Chill the paste in the fridge for 15-20 minutes, then roll it into small balls (about ¾ -1 teaspoon each). Freeze the balls for 30 mins for easier handling during assembly.

In a mixing bowl, combine glutinous rice flour with warm water, adding the water gradually. Mix until a dough forms. Knead the dough for 5 minutes until smooth and pliable. Cover with a damp towel to prevent drying. Pinch off a small piece of dough (about 15g each) and flatten it into a disc. Place a ball of black sesame filling in the center, then carefully wrap the dough around it, sealing the edges. Roll into a smooth ball. Repeat with the remaining dough and filling.

In a medium pot, bring water, coconut milk, sugar, ginger slices, and pandan leaf (if using) to a boil. Simmer for 10 minutes to infuse the flavors.

Bring a separate pot of water to a boil. Add the glutinous rice balls and cook until they float to the surface, about 3-4 minutes.

Transfer the cooked rice balls to a bowl and ladle in the coconut ginger soup. Garnish with black sesame seeds.