Prep: Preheat the oven to 475 F. Line two 18-by-13 inch baking sheets with parchment paper.
Scald the milk: Heat milk in a small saucepan to about 180 F, or until tiny bubbles form on the edges. Transfer milk to a large bowl and let it cool completely before proceeding.
226 grams whole milk
Make the dough: Whisk the sourdough discard, instant yeast and sugar into the cooled milk until completely dissolved.
75 grams sourdough discard, 50 grams brown sugar, 7 grams instant yeast
Fold the bread flour and salt into the mixture until all of the flour is hydrated.
390 grams bread flour, 8 grams salt
Knead the butter into the dough one tablespoon at a time. Your dough will gradually feel less oily as the butter is absorbed.
28 grams unsalted butter
Strengthen the dough: Turn the dough out on a clean, lightly-floured work surface and knead for 5 to 10 minutes. Developing gluten is key for smooth and shiny pretzels so make sure your dough is completely smooth before you stop kneading.
Bulk fermentation: Round the dough into a tight ball and place it in a clean, lightly-oiled bowl. Cover the bowl with plastic wrap and let the dough rise in a warm place, untouched for 20 minutes. Your dough should be slightly puffy but not doubled in volume.
Preshape the dough: Turn the dough out on a clean work surface and divide it into 10 equal portions. Round each piece of dough into a tight ball. Cover the dough with a large piece of plastic wrap.
Working with 1 piece at a time, lightly coax the dough into a 4-inch baton. Cover the preshaped dough with plastic wrap, let them rest for 15 minutes.
Shape pretzels: Working with one portion of dough at a time, roll it into an 24 to 30-inch rope with tapered ends.
Grab the tips and form a U shape. Twist the ends twice, and flip them over.
Tack the ends to the sides and place the shaped dough on a baking sheet.
Place shaped dough on baking sheets. Freeze the shaped dough for 10 minutes.
Baking soda bath: In a large glass or stainless steel bowl, dissolve baking soda in hot water.
20 grams baking soda, 452 grams water
Working with one portion of dough at a time, carefully submerge frozen dough in the baking soda bath for 1 minute. Transfer to a wire rack to drain.
Return pretzel dough to baking sheets. Sprinkle pretzel salt on pretzels while the surface of the dough is still wet.
20 grams pretzel salt
Bake: Bake for 10 to 15 minutes or until the pretzels are evenly browned. Transfer the pretzels to a wire rack.
Brush warm pretzels with butter.
42 grams unsalted butter
Enjoy: These are best eaten fresh from the oven the day they are baked. Enjoy them on their own or with a side of mustard.
Store: Store any leftover pretzels in an airtight container for up to 3 days.