Mix everything except flour. Add warm water, sourdough starter, brown sugar, yeast, and salt and stir to combine in the bowl of your stand mixer fitted with the paddle attachment.
Add half of the flour. Add 2 cups of all-purpose flour and stir to combine.
Add butter. Add 4 tablespoons (½ stick) of the melted butter, and stir.
Add rest of flour. Switch out the paddle attachment for the dough hook and slowly add the rest of the flour, ½ cup at a time, stirring and stopping to push the sides down to make sure the flour is fully incorporated. Repeat this process until the flour has been incorporated and the dough removes itself from the bowl’s sides. You want the dough to be slightly tacky but soft.
Knead dough. Set your mixer to medium and allow the dough to knead for 3-5 minutes.
Rise. Remove the dough, cover it with a tea towel or plastic wrap, and allow it to rise for 1 ½ hours or until doubled in size.
Prep baking sheet. Place a piece of parchment paper onto a baking sheet and set aside.
Divide dough. Once the dough has risen, turn the dough out onto a clean, dry surface and divide the dough into 12 equal portions. Shape the balls into a rope and cut them into 3 equal portions, creating 36 pieces. Transfer the pieces to the prepared baking sheet.
Prep pot and oven. Add the 6 cups of water, baking soda, and brown sugar in a pot over medium heat and bring to a boil. Preheat the oven to 425°F.
Boil. Once the water comes to a boil, work in batches to add the dough pieces into the water bath, boiling each batch for 3 minutes. Use a slotted spoon to remove the bites and place them on the baking sheet. Repeat until all dough bites have gone through the water bath.
Top pretzel bites. With the remaining 2 tablespoons of butter (remelt it if necessary), brush the tops of the dough bites with the remaining butter and sprinkle with pretzel salt.
Bake. Bake at 425°F for 8-12 minutes (8 minutes will give you a softer pretzel bite, and 12 minutes will give you a crunchier pretzel bite).