In a bowl whisk together flour and salt and press a little hole in the middle. In another bowl mix 100 ml warm water with the yeast and sugar and pour it in the small flour-hole. Let the yeast react for about 15 minutes.
Now add the rest of the warm water (250 ml) and knead until dough is smooth. Put in a bigger clean bowl, cover with wrapping and let it rest in the fridge for 2 hours.
Prepare a baking pan with baking paper and preheat oven to 180°C. Knead the dough again and divide into 7 pieces (á 140 grams). Take one piece and roll it into a 40-50 cm long line. Roll the ends of the lines a little bit thinner then cross them until you get the typical shape.
Now boil 2 liters of water together with the baking soda. Let it boil for 10 minutes. One after another put the pretzels into the boiling water for 30 seconds, then remove them with a skimmer and put them onto the baking sheet. Sprinkle with sea salt.