Pull apart rolls get an upgrade with sourdough starter!
Place all dough ingredients in the bowl of stand mixer fitted with the paddle attachment. Mix until a rough dough forms. Switch to the dough hook and knead on medium-low speed until the dough is quite elastic, about 10-15 minutes. Resist the urge to add more flour - you want the dough to be very soft.
Transfer the dough to a large, buttered bowl. Cover and allow to rise at room temperature for 8-12 hours, or until doubled.
Gently deflate the dough and divide it into 16 equal pieces. Grab the corners of one of the pieces and pull it towards the middle. Roll the ball, seam side down, on your work surface to create surface tension. Place in a buttered 13x9-inch baking dish. Repeat with the remaining dough.
Cover the pan and allow to rise at room temperature for 6-8 hours, or until the rolls are quite puffy and fill the pan.
30 minutes before you plan on baking the rolls, preheat your oven to 375° F. Bake the rolls for 20-25 minutes, or until they're deep golden brown and register 200° F when an instant read thermometer is inserted into the center of a roll.
Remove from oven and brush the tops of the rolls with the melted butter. Serve warm with grass-fed butter.
An active sourdough starter means that it has been fed 8-12 hours beforehand and is bubbly and passes the float test.