In a stand mixer fitted with a dough hook, combine all the dough ingredients except the butter.
370 g bread flour, 15 g granulated sugar, 7 g instant dry yeast, 7 g sea salt, 100 g whole milk, 1 large egg, 150 g russet potatoes
Knead at medium speed for 10-15 minutes. Initially, the dough will be dry and crumbly. As the potatoes fully integrate, they release moisture and starch, which helps bind the ingredients together and gradually transforms the mixture into a soft, cohesive dough.
Gradually add cubed butter, one piece at a time, while continuing to knead.
50 g unsalted butter
Scrape down the sides of the bowl and continue to knead for 10-20 minutes until the dough is smooth, elastic, and passes the window-pane test.
Transfer the dough to a clean, lightly oiled bowl, cover it with plastic wrap, and let it proof for about 90 minutes at around 77℉ (25℃) until doubled in size.