Into the mixing bowl of the stand mixer weigh the milk or water. Next, add the sourdough starter. Which should float nicely atop the liquid. Whisk until fully incorporated and bubbly.
Weigh/add the rest of the ingredients. Make sure to add the salt on top of the flour, as salt has the potential to kill the yeast when in direct contact. With clean hands, mix until a shaggy ball forms and cover, and allow to autolyze for 15-30 minutes.
After allowing the dough to rest, knead the dough on medium-low speed in the stand mixer with a dough hook. Watching that a nice dough ball forms and is not sticking to the sides of the bowl. If after 5 minutes, the dough is not fully pulling away from the bowl, add a tablespoon of flour at a time, until it pulls away. Knead for about 15-20 minutes until a smooth, elastic dough forms. The dough should also pass the window pane test.
After your dough is properly kneaded, allow it to rise in a greased bowl covered for 12-24 hours at no higher than 75 degree Fahrenheit. The temperature in the room, and the ambient temperature of the dough directly effects the time it will take for your dough to rise. If sourdough has taught me anything, it would be, not to rush this process, slow down and let time create a lustful depth of flavor. I love to allow my dough to rise overnight. Something magical happens to dough in that quiet, darkness.
The next day, divide your dough. Start by weighing the dough and dividing by 12. Then, equally weigh out each piece of dough with a bench scraper. To shape, pull all the sides of the dough into the center and flip, shaping into a tight ball.
Butter the inside of the cast iron or baking dish, and place each ball into the baking dish, giving them a little room for expansion.
Preheat the oven to 375℉. Cover and let rise for another hour or two. Again, time always depends on temperature. At the end of the second rise they should be nice and puffy.
With a pair of scissors, make a small cut in the center of each roll. Brush with the melted butter, and sprinkle with sea salt. Place them in the oven. Bake for 20-30 minutes or until golden brown and a buttery fragrance wafts through the house.
Allow to cool, & Bon Appétite!