In a large bowl, combine the sourdough starter and water. Mix until the starter is mostly dissolved.

Add the flour and sprinkle the salt over the top. Mix until a shaggy dough forms and no dry flour remains. Cover and rest for 30 minutes.

Perform two sets of stretch and folds, spaced 30 minutes apart. With a wet hand, stretch one side of the dough upward, fold over the top, rotate, and repeat on all four sides.

Before the third stretch and fold, grate the chilled butter using a microplane or box grater. Add 15 grams of grated butter, fold the dough over itself, rotate the bowl, and add another 15 grams. Repeat until all 60 grams have been incorporated across four folds.

Cover and bulk ferment until the dough has nearly doubled and feels soft and jiggly, about 3 to 8 hours depending on kitchen temperature.

Lightly grease a standard 12-cup muffin tin (or a 9-inch round cake pan for pull-apart style). Turn the dough onto a lightly floured surface and divide into 12 equal portions, about 90-95 grams each.

Shape each piece into a smooth ball by pulling the edges underneath to create surface tension. Place one in each muffin cup, seam side down.

Preheat oven to 450°F. Bake the rolls uncovered for 5 minutes. Remove from oven and score the top of each roll with a simple slash.

Return to oven and bake an additional 20 minutes, until deeply golden brown (internal temperature around 200°F). Cool in the pan 5 to 10 minutes before transferring to a wire rack.