Combine water, yeast, and brown sugar in a small bowl. Whisk to combine and let stand until the yeast begins to activate and foam slightly.
Bring 2 quarts of water to a boil over high heat. Add the baking soda and using a perforated spautula, lower one pretzel at a time into the water. Boil about 30-45 seconds and remove to a paper towel for a minute to drain. Place three pretzels on each baking sheet and brush well with the remaining 2 Tbsp melted butter and sprinkle generously with salt.
Yields 6 pretzels.