A liquid seeds: high-gluten flour 160g, fresh milk 180g, and yeast 2g.

B Dough: 400g of high-gluten flour, various liquids, 5g of yeast, 85g of sugar, 6g of salt, egg 1, fresh milk 145g, 50g of butter.

1. First, make liquid seeds, put the materials of liquid seeds into a clean basin, stir them evenly, put the dough at room temperature to foam, and then put it in the refrigerator for more than 16 hours.

2. Put all the materials of dough B except butter into the chef's machine, stir until the expansion stage, add butter, and knead the dough into a film (as shown in glove film).

3. Knead it smooth, put it in a pot and ferment it in a warm place to double its size.

4. Ventilate the fermented dough, evenly divide it into 4 parts, cover it with plastic wrap and wake it for about 15 minutes, roll it out, roll it up again, and repeat it twice.

5. Roll into strips, spread with purple potato paste, roll up and put into a toast mold, ferment in a warm place until toast box is 9 minutes full, and brush the surface with egg yolk.

6. Bake in the oven 170 degrees for 45 minutes. The surface must be covered with tin foil to avoid baking.

7. Take it out after baking, put it on the baking net to cool, and put it in a fresh-keeping bag to seal it. Eat it as soon as possible.