Line a baking sheet with foil and preheat an oven to 250 degrees F. Spread 1 box of baking soda in an even layer on the tray. Bake for 1 hour and then allow to cool to room temperature. Store in an airtight container in a cool, dark location.
Mix together the beer and milk in a measuring cup and microwave for about 45 seconds, until just barely warm. Combine the beer/milk with the yeast and sugar in the bowl of a stand mixer fitted with the dough hook. Once the mixture is foamy (after about 5-7 minutes), and the flour, 4 tablespoons of the melted butter, egg, and salt and mix on medium speed for about 10-15 minutes, until the dough is smooth.
Lightly oil the mixing bowl, toss the dough to coat lightly in oil, and cover with plastic wrap. Place in a warm-ish location and allow the dough to rise for 2 hours, until at least doubled in size.
Transfer the dough to a clean work surface (do not flour). Using a scale, divide the dough into 8 equal portions (I did 120 g pieces). Like a baking sheet with a silicone baking sheet and cover with plastic wrap.
Working quickly, roll each piece of dough into a rope about 12" long. Tie into a knot and tuck the ends in (see video above), and place each knot under the plastic wrap on the prepared baking sheet. Repeat with remaining dough. Allow dough to rest for 20 minutes. Preheat an oven to 425 degrees F in the meantime.
Combine 6-8 cups of water with the baked baking soda in a dutch oven or pot, and stir to dissolve. Heat the water until steaming, but not boiling. Turn off the heat.
Gently transfer 2-3 of the knots to the steaming water for about 30 seconds, stirring gently to make sure the dough is well coated. Using a slotted spoon or spider, lift the knots from the water, allow a bit of the water to drain off and transfer to the silicone lined baking sheet. Repeat with remaining dough.
Brush knots with egg wash and top with pretzel salt or coarse kosher salt. Bake for 15-17 minutes, until golden brown, rotating the baking tray halfway through. Remove from the oven and brush with the remaining 2 tablespoons of melted butter. Allow to cool slightly, serve warm.