Active the yeast: Whisk the brown sugar, water and active dry yeast together. Cover the bowl and let the yeast activate for 10 to 15 minutes until the mixture appears foamy.
113 grams water, 7 grams active-dry yeast, 25 grams dark brown sugar
Make the dough: Whisk the wet ingredients into the yeast mixture.
56 grams milk, 113 grams sourdough discard
Fold the bread flour and salt in until no dry traces of flour remain.
360 grams bread flour, 6 grams salt
Knead until a cohesive dough forms, about 3 minutes.
Knead the butter into the dough 1 tablespoon at a time. The dough will initially feel greasy and get progressively smooth and less sticky as the butter is absorbed. This may take a few minutes. Cover the dough and let it rest for 20 minutes.
28 grams unsalted butter
Prep: Preheat the oven to 420 F and line a large baking sheet (18 by 13 inches) with parchment paper.
Strengthen the dough: Knead the dough for 5 to 10 minutes, try your best to get the dough to appear as smooth as possible, or your pretzel buns will have a wrinkly appearance once baked.
Shape the dough: Divide the dough into 6 even portions. Working with one portion of dough at a time, flatten the dough into a rough rectangle, fold the corners towards the center and pinch the seam shut. Flip the dough over, cup it with the palm of your hand and drag it on the surface in a circular motion until the seam on the bottom is completely sealed and the surface of the dough appears taut and smooth.
Arrange the dough on the baking sheet. Flatten the dough and cover with plastic wrap to prevent the dough from drying out.
Water bath: Bring water to a boil and transfer to a large heat-proof mixing bowl. Whisk the baking soda into the hot water until completely dissolved.
64 oz water, 60 grams baking soda
Working with one portion at a time, dip the dough into the baking soda bath. Using a spatula or your fingertips, keep the dough submerged in the water for 1 minute. Transfer the dough to a wire rack and drain any excess moisture for a few minutes.
Return the dough to the prepared baking sheet. Repeat with the remaining portions of dough. Arrange the dough a few inches apart, they won't rise a lot but this will prevent them from sticking together.
Sprinkle pretzel salt on top of the buns. Using a lame fitted with a sharp blade or a paring knife, score an “X” on top of each bun.
15 grams pretzel salt
Bake the buns: Bake the pretzel buns at 420 F for 5 minutes. Turn the temperature down to 375 and continue baking for 10 to 15 minutes or until the buns appear a dark, golden brown and the center of the buns measure 190 to 200 F when probed with an instant-read thermometer.
Serve: Brush the baked buns with butter and serve.
14 grams unsalted butter
Store: There buns are best enjoyed the day they are baked, especially if you're using pretzel salt. Store any leftovers in a brown paper bag for up to 2 days.