Sourdough Potato Buns

Name: Sourdough Potato Buns
Prep time: 40 min
Cook time: 15 min
Total time: 55 min
Ingredients: 1 medium (8oz, 224g) russet potato; 1 1/2 cups (12 oz, 360ml) whole milk; 2 tablespoons (1 oz, 28g) unsalted butter; 2 tablespoons (1 oz, 28g) granulated sugar; 1 1/2 teaspoons table salt; 1 large egg; 1 cup (8oz, 224g) active sourdough starter (100% hydration); 3 cups (15 oz, 425g) bread flour; 1 egg for brushing; Sesame seeds for garnish (optional)