Prepare Tangzhong by whisking together 2 tablespoons of bread flour and 1/2 cup of water over medium heat until thickened, about 2-3 minutes. Cool completely, best refrigerated for 30 minutes.

In your stand mixer bowl, combine 3 cups of bread flour, 2 tablespoons of sugar, 1 teaspoon of salt, 2 teaspoons of instant yeast, and 2 tablespoons of milk powder. Add the cooled Tangzhong and 1 large egg. Gradually pour in 1/2 cup of milk while mixing on low speed. Knead for 12-14 minutes until smooth and elastic.

Shape the dough into a ball, oil the surface, and cover it. Let it proof in a warm area for about 1 hour until doubled in size.

Prepare the garlic butter filling by mixing minced garlic and chopped green onions with softened unsalted butter and a pinch of salt.

Roll out the proofed dough into a rectangle, spread the garlic butter filling, sprinkle the green onions, roll tightly, and pinch seams to seal.

Place the rolled dough seam side down in a parchment-lined loaf pan. Cover and let it rise for about 35-40 minutes.

Prepare an egg wash, brush it over the top of the loaf, and bake at 350°F for 25-30 minutes until golden brown.

Allow it to cool in the pan for 5 minutes before transferring to a wire rack and cooling completely before slicing.