In a large bowl, stir the water and barley malt syrup until dissolved, then sprinkle in the instant yeast. Let stand until foamy, 5–7 minutes.
Add the bread flour and fine sea salt to the bowl and mix to form a shaggy dough. Knead on a lightly floured surface (or with a dough hook) until smooth and elastic, 8–10 minutes. Knead in the softened unsalted butter until fully incorporated, 1–2 minutes.
Shape the dough into a ball, place in the bowl, cover, and let rise at room temperature until doubled, 60–75 minutes.
Turn the dough out and divide into 8 equal pieces. Roll each into a short log, cover, and rest 10 minutes to relax the gluten.
Line two baking sheets with parchment. Roll each piece into a 24–26 inch rope with tapered ends, leaving a thicker center. Form a U-shape, cross the ends twice, then fold them down to the bottom of the U and press firmly to adhere, creating the pretzel shape. Set on the prepared sheets.
Freeze the shaped pretzels until firm to the touch, 20–30 minutes. Meanwhile, preheat the oven to 450°F (230°C).
Wearing gloves and eye protection, prepare the lye bath in a nonreactive container: pour in the cold water, then slowly sprinkle in the food-grade sodium hydroxide (lye) while stirring until fully dissolved. Never add water to lye, and avoid aluminum.
Working one pretzel at a time, dip into the lye bath for 10–15 seconds, spooning solution over the top. Lift, let excess drip off, and return to the parchment-lined sheet.
Using a sharp knife or razor, score a 4–5 inch shallow slit (about 0.5 inch deep) along the thick bottom belly of each pretzel. Sprinkle the tops with pretzel salt to taste.
Bake until deeply mahogany-brown and shiny, 12–15 minutes, rotating the sheets halfway. The crust should feel set and sound hollow when tapped.
Cool on racks 5 minutes before serving. Enjoy warm the day they’re baked.