Mix in the glass of a mixer or a large container the flour with the yeast and the salt. Add the slightly warm water (do not burn) and work everything until incorporated. If it is done by hand, cover and let it rest for 20-30 minutes before starting to knead, as it will be easier (autolysis).
Knead by machine or by hand with energy and patience, trying not to add more flour until little by little an elastic and homogeneous dough is formed, moist but not stickywell cohesive. If it were really indomitable, flour the work surface very little by little, as it is a dough that must be very hydrated.
Once you have the elastic textureForm a ball, place in a lightly oiled container and cover with film or a shower cap. Let rise until doubled in size, about 1-2 hours depending on room temperature.
Meanwhile, make the icing heating the water with the flour, the pinch of sugar, the baking soda and the salt in a small saucepan; cook over medium heat, stirring, until it reduces a little and acquires a bright tone, like a syrup, Reserve.
Flour the work surface and degas the dough. Divide into two portions and reserve one aside, covered with film or a clean cloth. Stretch the other with a roller or your hands until leaving a thickness of not more than 1 cm, giving it an oblong shape. Take a sheet of baking paper, cover with film and do the same with the other dough.
Preheat the oven to 230ºC with heat up and down and let the loaves rest for 30 minutes. After the time, carefully mark the parallel lines on the dough, using your fingers or a wooden spoon with a cylindrical handle (it can be greased with oil if it sticks).
paint with icing, sprinkle with the seeds and bake for 15-20 minutes, until well browned and slightly toasted, without burning. While it is baking, repeat the process with the other half and cook when the first loaf is ready and cooling.