Place the flour, salt, brown sugar, yeast, and warm water in the bowl of a stand mixer fitted with the hook attachment and beat until well combined. Knead the dough, by hand or by machine, until it’s smooth and soft, 5 to 7 minutes. Flour the dough a little, place on a floured surface, and cover. Let rest for 30 minutes.
Preheat the oven to 475°. Prepare a baking sheet with parchment or cooking spray.
Uncover the dough and divide it into 8 equal pieces. Let them rest uncovered for another 5 minutes.
Using the palms of your hands, roll each piece into a thin rope about 25 to 30 inches long. Twist each rope into a pretzel shape by lifting the ends of the rope, crossing them to make a twist, and then folding them back down on the bottom loop. Gently press the ends so they stay in place.
Boil 6 to 8 cups of water in a large stockpot and add the baking soda, stirring until it’s dissolved. Reduce to a simmer. Working quickly and carefully, dip each pretzel into the water and simmer for 30 seconds on each side, flipping them with a slotted spoon. They will puff up slightly in the water.
Transfer to a prepared baking sheet and sprinkle with kosher or coarse sea salt. Bake pretzels until golden brown, 8 to 10 minutes.
Remove from the oven and brush with melted butter until the butter is gone. These pretzels are best consumed while warm. They can be reheated in the oven, or frozen and defrosted later in a low oven. Top with your favorite mustard, if desired.