In the bowl of a stand mixer, combine the sourdough starter, warm water, softened butter, salt, brown sugar, and all-purpose flour. Start mixing on low speed until the dough forms a sticky ball.

Once combined, knead the dough on high speed for 5 to 10 minutes. The dough should be slightly sticky but manageable. You’ll use more flour later during shaping, so resist the urge to over-flour the dough now.

Grease your hands, remove the dough from the mixer, and shape it into a ball. Place it in a large greased bowl and cover with plastic wrap (using a clean towel is recommended by some, but I don't suggest this because the dough can dry out with this method.) Let it rise for 8 to 10 hours, or until doubled in size.

After the dough has doubled in size, turn the risen dough out onto a lightly floured surface. Press it gently to remove air bubbles. Divide the dough into 6 equal pieces using a bench scraper or knife. I find it easiest to divide it into strips, this makes it easier when rolling into a rope.

Roll each piece into a rope about 30 to 35 inches long, roughly the thickness of your finger.

When rolling, it can be helpful to pick the dough up and allow gravity to help stretch the dough. You can also hold both ends and stretch the dough while gently hitting it against the work surface

To shape into pretzels: Form a U shape with the dough. Twist the ends together twice. Fold the twisted ends down and press into the bottom of the U to form the classic pretzel shape. If you prefer, skip the twisting and cut the dough into bite-sized pieces to make pretzel bites instead.

In a shallow dish, mix ¼ cup baking soda with 3 cups of boiling water. Mix until most of the baking soda is dissolved. It's okay if it doesn't all dissolve.

Dip each shaped pretzel or pretzel bite into the solution for 10 seconds using a slotted spoon. They will become very soft and puffy after the baking soda bath. Handle carefully, they can tear easily at this point.

Place pretzels on a parchment-lined baking tray and immediately sprinkle with sea salt, kosher salt, or coarse pretzel salt.

Preheat your oven to 450°F. Bake for 12 to 15 minutes, or until pretzels are a deep golden brown.

Remove from the oven and brush the tops generously with melted butter using a pastry brush. Serve warm with mustard, cheese dip, or your favorite pretzel accompaniments.