1. Combine Wet Ingredients and Starter: In a large mixing bowl, whisk together the active sourdough starter, warm water, granulated sugar, and salt until well combined. The mixture should look slightly milky and have a few bubbles from the active starter.

2. Form the Dough: Gradually add the all-purpose flour to the wet ingredients, mixing with a wooden spoon or your hands until a shaggy dough forms. Once most of the flour is incorporated, turn the dough out onto a lightly floured surface.

3. Knead the Dough: Knead the dough for about 5-7 minutes until it becomes smooth and elastic. It should spring back slightly when poked. If the dough is too sticky, add a tiny bit more flour, a tablespoon at a time.

4. First Rest: Place the kneaded dough back into the clean mixing bowl, cover it with a kitchen towel or plastic wrap, and let it rest in a warm place for 30 minutes. This allows the gluten to relax, making the dough easier to shape.

5. Shape the Pretzels: Divide the dough into 8-10 equal pieces. Roll each piece into a long rope, about 18-24 inches long and 1/2 inch thick. To form the classic pretzel shape, make a U-shape with the rope, cross the ends over each other twice, and then bring the ends down to attach them to the bottom curve of the U. Gently press to seal.

6. Prepare for Boiling: Preheat your oven to 450 F (230 C). In a large pot, bring 8 cups of water to a rolling boil. Carefully add the baking soda to the boiling water (it will foam up, so use a large pot). Line a baking sheet with parchment paper and lightly grease it.

7. Boil and Bake: Carefully drop one or two pretzels into the boiling baking soda solution for 30 seconds per side. Using a slotted spoon, remove the pretzels, allowing excess water to drip off, and place them on the prepared baking sheet. Brush each pretzel with melted butter and generously sprinkle with coarse sea salt.

8. Final Bake: Bake the pretzels for 12-15 minutes, or until they are golden brown and puffed. The color is your best indicator of doneness; you want a rich, deep golden hue.