Preheat the oven to 350°F and prepare a sheet pan lined with parchment paper.

In a saucepan, combine the milk, butter, sugar, and salt. Bring it to a simmer over medium heat while stirring occasionally.

Once the mixture comes to a simmer, take it off the heat and stir in the vanilla. Immediately sift in the 35 grams of all-purpose flour and whisk the mixture until it thickens to a baby food consistency and becomes as smooth as possible. Some small lumps are okay.

After the all-purpose flour have been incorporated, add the tapioca flour and fold everything together until no more dry flour is visible. The dough will become quite stiff and thick. Let the dough cool until it's warm to the touch.

Once the dough has cooled, add the beaten egg in 3 additions and incorporate the egg completely with a spatula before adding the next. After each addition of eggs, check the consistency of the dough. A proper dough will flow slowly like thick batter, looks slightly translucent, and forms a triangular shape when it breaks off.

After the dough is at its proper consistency add the toasted black sesame seeds. Fold the mixture to evenly disperse the sesame seeds. Transfer the dough to a piping bag fitted with a round piping tip.

Pipe the dough out into a 1½ inch wide dome, about 1 inch in height. Keep each piping about 1 inch apart to accommodate for some puffing up when baking. Dip your finger into some cold water and dab the tips of each dough dome to round it off.

Bake the mochi breads for about 25 to 30 minutes or until it turns slightly golden brown. Let cool for a few minutes and enjoy!