Peanut Streusel
1. In a bowl, cream the butter and peanut butter until smooth. Add the sugar and mix until incorporated. Add the yolk and vanilla extract and combine. Add the all purpose flour, baking powder, and cornstarch and mix until a cohesive dough forms.

2. Break the dough apart into small crumbly, pieces. Cover and set aside at room temperature until needed.

Flour Paste/Tangzhong
1. In a microwave safe bowl, whisk the water and bread flour together until there are no lumps. Microwave at 20 second intervals, whisking inbetween, until the mixture is thick and smooth like a pudding.

Dough
1. In the bowl of a stand mixer, add the cooked flour paste/tangzhong and slowly whisk in the milk. Whisk in the egg and mix until smooth. Add the bread flour, sugar, salt, and yeast and mix with a spatula.

2. Once the dough roughly comes together, place the dough hook on the stand mixer and mix on medium low speed for 5 minutes.

3. Fold in the butter by hand. Once the butter is roughly incorporated, continue kneading with the dough hook on medium low for 5 minutes.

4. Flour your hands and form the dough into a ball. Transfer to a bowl that’s been lightly greased with oil. Cover and place is a warm place. Let rise for 40 minutes to 1 hour and 15 minutes or until doubled in size.  To test if it’s ready, flour your index finger and press into the dough, like you’re poking someone. If the dough springs back, let it rise for a little longer. If the indentation remains, the dough is ready. 

5. Line two baking sheets with parchment paper.

6. Once the dough has doubled in size, divide the dough into 12 equal pieces (around 40 g each in weight). Shape each piece into a smooth round. If the dough feels too sticky, generously flour your hands. Let rest for 10-15 minutes.

7. Meanwhile mix 1 cup water with 1 teaspoon cornstarch.*

8. Generously flour your hands. Get one piece of dough and stuff with a heaping teaspoonful of peanut streusel.* Pinch the sides of the dough to seal. Repeat until all the dough pieces are filled. 

9. Dip the smooth side of the dough into the water-cornstarch. Scoop two heaping tablespoons of peanut streusel on the countertop and press the wet part of the dough into the streusal. Make sure to stick as much of the streusel onto the dough as possible. Repeat with the rest of the dough.

9. Place six pieces of dough on each baking sheet. Carefully reshape each dough into a circle if needed. Loosely cover with plastic wrap and let rise in a warm place for 40 minutes to 1 hour.

10. Preheat oven to 375 degrees or 190 degrees C.

11. Bake for 13-15 minutes, rotating sheets halfway through baking, or until lightly golden. Cool on a rack and enjoy warm or at room temperature. Store in an airtight container for up to 3 days.