Whisk the flour and water in a small saucepan over medium-low heat for 3–4 minutes to make a paste. Mix them. Flour, sugar, yeast, and salt in a stand mixer
Add egg, milk, tangzhong, and vanilla. Low-speed dough hook knead until a shaggy ball develops. Knead dough. Slowly add 1 tablespoon of softened butter.
Place the dough ball in a large greased basin. Cover the top with plastic wrap and let it rise for an hour. Fill peaches.
Over medium heat, mash peaches, sugar, and lemon juice. Cook for 1 minute after adding cornstarch slurry. Cool the jam.
Spread dough. Roll dough into an 18x15-inch rectangle on a lightly floured surface. Spread cinnamon filling.
Scatter thinly sliced peaches on top.
Roll, cut. Cut 12 1-1/2-inch strips of dough. Roll strips away from you toward the clean end. Put them in the baking dish.
Bake! Spread the crumb topping evenly. Bake them for 30–35 minutes in the preheated oven until the tops are golden brown