In a small microwave safe bowl or liquid measuring cup, combine the milk and butter. Microwave on high for about 1 minute, until the mixture is warm to the touch (about 120-130°F). The butter does not need to melt completely, but it should be soft. Transfer the milk and butter to the bowl of your stand mixer.
To the butter and milk mixture, add 1 cup of bread flour, sourdough starter, egg, honey, yeast, and salt. Using the paddle attachment, beat for 2 - 3 minutes on medium speed, until the mixture is very smooth.
Switch to the dough hook and gradually add the remaining bread flour while mixing on the lowest speed. Continue to mix until the dough comes together and forms a smooth ball, approximately 4 - 5 minutes.
Transfer the dough to a lightly oiled bowl, turning to coat each side with oil. Cover and let rise until the dough almost doubled and the imprint of two fingers remains.
Punch down the dough and divide into 12 equal portions. Shape into rolls (round, oval, etc.) and place on baking sheets lined with parchment paper or silicone mats. Cover and let rise until puffy, about 30 minutes.
While the rolls rise, preheat the oven to 400°F.
Optional: before baking, brush the rolls with egg wash (1 egg beaten with about 1 teaspoon of water) and sprinkle with sesame seeds. Slash with a sharp knife, if desired.
Bake the rolls for 15 - 17 minutes, until golden on top and hollow sounding when tapped lightly. Let the rolls cool on the pan for 10 minutes, then transfer to a wire rack to cool completely.