In a mixing bowl, combine the sourdough starter, flour, salt, and sugar.
Gradually add warm water until a dough forms.
Knead the dough on a floured surface for about 5-10 minutes.
Place the dough in a greased bowl and cover it with a cloth.
Let the dough rise for about 1 hour, or until doubled in size.
Preheat the oven to 450°F (230°C).
Divide the dough into 8 equal pieces and roll each into a long rope.
Shape each rope into a pretzel form.
Prepare a baking soda bath by dissolving baking soda in boiling water.
Dip each pretzel into the baking soda bath for 30 seconds, then place on a baking sheet.
Sprinkle with coarse sea salt and bake for 12-15 minutes until golden brown.