Add the flour, sourdough, water, salt, and egg to the mixing machine bowl with the hook attachment.
Mix the ingredients for 5-6 minutes on slow until the dough starts to come together.
Increase the mixing machine’s speed and mix until the dough is fully developed.
Perform the windowpane test by stretch a small piece of dough until you can see through it.
Grease a larger bowl and transfer the dough into it.
Cover the dough somewhere warm in your kitchen and let it ferment for about 4 hours.
When your dough reaches 2 hours, stretch and fold the dough in the bowl. This step is supposed to regulate the dough temperature and further strengthening the dough by aligning the gluten network.
Once the fermenting of the dough is finished, cut the dough into 6 portions or scale them individually at 95 grams.
Round each dough piece into a ball shape and place onto a lined baking tray.
Slightly flatten the dough balls.
Cover the dough with plastic and allow it to proof until double the size or about 90 minutes.
Preheat the oven to 190°C or 375°F, thirty minutes before baking.
When he buns are proofed or doubled in size, brush them with the beaten egg.
Decorate the buns with sesame or poppy if you wish.
Bake the buns for about 18-20 minutes or until they are light golden brown.
Remove them from the oven and cool on a wire rack before serving.
You can keep your sourdough buns fresh by packing them in a bag for up to 5 days or you can freeze them for up to 30 days.