In the bowl of a stand mixer fitted with the dough hook, combine the water, sugar, and yeast.
Add in the flours, melted butter, and salt. Mix on medium high spreed for about 5 minutes until smooth and passes the windowpane test.*
Place the dough in a large lightly greased bowl, cover, and proof overnight in the fridge or in a warm environment for about one hour or until doubled in size.
Once the dough has proofed, line a baking sheet with parchment paper. Line a second baking sheet with nine 4" individual parchment squares.
Divide the dough into 9 pieces, weighed about 85-90g.
To shape the pretzels, roll into a long, skinny rope (about 24" long). Take the two ends and cross them over each other three times, then bring the bottom U part of the dough over and pull the twist through to the top, slightly pressing the ends into the dough. (see photos above for reference)
Transfer the shaped pretzel to an individual parchment square, and repeat with the rest of the dough.
Cover the pretzels and proof for about 30 minutes.
Meanwhile, preheat the oven to 425 degrees F, and bring a pot of water to a simmer.
Once the pretzels have proofed, turn the water down to low heat and slowly add the baking soda.
Bathe the pretzels (about 2 at a time) for 30 seconds on each side, then place on baking sheet lined with parchment paper.
Brush each with an egg white and sprinkle with coarse salt.*
Bake for about 12-15 minutes until deeply golden.