Buttermilk Cluster

In the bowl of a stand mixer fitted with a dough hook, combine yeast, sugar, and ¼ cup water heated to 115°; let sit until foamy, about 10 minutes. Whisk in buttermilk and honey; add flour and salt. Mix on medium-low speed until dough forms a ball and pulls away from the side of the bowl, 6–8 minutes. (Sprinkle in a little water if dough seems dry.) Cover bowl with plastic wrap and set aside in a warm place to let dough rise until doubled in size, about 2 hours.

Heat oven to 400˚. Grease a 9" round springform pan with butter. Uncover dough; divide into 12 portions. Roll each dough piece into a ball; transfer ball to pan; repeat with remaining dough. Cover pan with plastic wrap and set aside to let dough rise until doubled in size, about 1 hour. In a small bowl, whisk together egg and 1 tsp. water. Uncover dough and brush egg mixture over the top; sprinkle with sesame seeds. Bake until golden brown and an instant-read thermometer inserted into the center of dough registers 190°, about 35 minutes. Transfer to a wire rack and let cool for at least 15 minutes before serving.