½ cup plus 3 tablespoons dark brown sugar, divided
1 stick (½ cup) unsalted butter, divided
Directions
Prepare a tangzhong: Add milk to a saucepan a place on the stovetop over medium heat.
When milk starts to steam, add 60 grams flour and whisk vigorously until the mixture resembles a paste similar to mashed potatoes. This will happen quickly.
Add tangzhong to the bowl of a stand mixer along with the remaining 300 grams flour, yeast, olive oil, 2 tablespoons vanilla extract, 1 teaspoon kosher salt, 1 tablespoon ginger powder, 1 tablespoon cinnamon, and 3 tablespoons dark brown sugar.
With the dough hook attached, mix on the stir setting until combined.
Increase the speed to the second setting and continue mixing for 10 minutes, until the dough is cohesive and clears the sides of the mixer. If needed, add additional flour 1 tablespoon at a time until the dough pulls off the sides of the bowl.
With the mixture still running, add 4 tablespoons butter, 1 pat at a time, to the dough until emulsified. This will take about 5-7 minutes.
Once the butter is incorporated, continue mixing for an additional 10-15 minutes until the dough wraps around the hook and is firm and elastic.
Transfer dough to a lightly greased bowl, cover, and let sit for 1 hour at room temperature. Next, refrigerate for 2-24 hours.
Preheat oven to 350 F.
Using 1 tablespoon butter, grease a loaf pan, line it with parchment, and grease the paper.
In a small bowl, combine the remaining 1 tablespoon vanilla, ¼ teaspoon kosher salt, 3 tablespoons room-temperature butter, 1 tablespoon ginger, 1 tablespoon cinnamon, and ½ cup brown sugar. Set filling aside.
Add dough to a lightly floured surface and pat it into a square.
Roll dough into a long rectangle, approximately 8x17 inches.
Cut into 8 even squares.
Spread a dollop of filling onto each square, leaving the edges clean.
Stack the squares, rotate the pile horizontally, and add it to prepared loaf pan.
Bake for 35 minutes until cooked throughout.
Let cool and garnish with sifted powdered sugar, if desired, before serving.