Make the dough: Dissolve the sourdough starter and barley malt syrup in the water. Stir the bread flour into the water mixture, a third at a time. The dough will feel dry, incorporate the butter into the shaggy dough and continue kneading until all of the flour is hydrated. Cover the bowl with plastic wrap and let dough rest for 1 hour.
Strengthen the dough: Turn the dough out on a clean work surface and knead for 5 to 10 minutes. Developing gluten is key for chewy pretzels so make sure your dough is completely smooth before you stop kneading.Your dough shouldn’t feel sticky, but if it does, coat your hands and work surface with a little bit of oil. 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 until doubled in volume, about 4 to 6 hours.
Cold proof: Deflate the dough, round it into a tight ball. Cover the bowl with plastic wrap and let the dough rest in the refrigerator overnight.
Pre shape the dough: The next day, divide the dough into 10 equal portions. Flatten the dough into a rough rectangle. Roll the dough tightly into a 6-inch log, cover the dough with plastic wrap and let it rest for 15 minutes.
Shape pretzels: Working with one portion of dough at a time, roll it into an 18-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.
Final proof: Let the shaped dough rise uncovered at room temperature for 1 hour or until the dough looks puffy, but not doubled. Place the dough in the freezer for at least 30 minutes.
Prep: Preheat your oven to 500 F. Line two baking sheets with silicone mats.
Lye bath: In a large glass or stainless steel bowl, dissolve 28 grams of food grade lye in 900 grams of cold water, use a stainless steel whisk to make sure all of the lye has dissolved. Using protective gear, carefully dip the frozen pretzel dough in the lye solution and submerge for 15 to 20 seconds. Place dough on prepared baking sheets, at least 2 inches apart.
Bake: Sprinkle pretzel salt on pretzels while the surface of the dough is still wet. Score the dough using a lame or a sharp knife. Turn the temperature down to 450 F and bake for 15 to 20 minutes or until the pretzels are evenly browned. Transfer the pretzels to a wire rack.
Enjoy and store: Enjoy freshly baked pretzels warm with butter or sweet brown mustard. These are best eaten the day they are baked, store any leftover pretzels in an airtight container for up to 3 days.