Combine unsalted butter, salt, sugar, and milk in a saucepan. Melt on low heat.
Add all-purpose flour all at once and stir until combined.
Cook until the flour starts to thicken and gelatinize.
Add tapioca starch and stir until combined.
Add eggs gradually, starting with about 50 grams.
Check the batter consistency: when lifted with a spatula, it should flow down smoothly, leaving some hanging in a long "V" shape.
Stir in toasted black sesame seeds.
Transfer the batter to a piping bag.
Pipe the batter onto a baking sheet lined with parchment paper, making rounds about 2-2 1/2 inches wide. Keep them at least 2 inches apart as they will expand.
Dip your finger in water and smooth the pointy top of each round.
Bake at 375°F (190°C) in a conventional oven, or 350°F (180°C) in a convection oven, for 30 minutes.
Let them cool slightly and serve warm.
Notes
Please refer to the video link for comprehensive cooking instructions.