Dissolve the sugar in the warm water. Sprinkle the yeast over the top of the water and allow that to sit and foam up for 5-6 minutes.

In a large bowl, combine the salt, bread flour, and all-purpose flour. Pour the yeast water into the bowl. Stir until combined. Turn out onto a floured surface and knead for 5-6 minutes. This flour is probably more water-based than you might be used to (if you bake bread often), so feel free to really flour your hands or the surface as you work. Place in an oiled bowl, cover, and allow to rise for 1 hour (or until doubled in size).

Fill a large pot with 3 cups water and 3 tablespoons baking soda. Stir to dissolve. Heat the water to a low boil. While the water heats up, on a floured surface, divide the dough into small balls, or roll into long ropes and shape like pretzels.

Place each pretzel in the boiling water for 30 seconds, flipping halfway through cooking. Use a slotted spoon to remove them from the water, draining away as much water as you can. Place on a baking sheet lined with parchment paper. Allow to rest for 15 minutes.

Brush the tops of the pretzels with melted butter and sprinkle on the sea salt. Bake at 375°F for 20-25 minutes. The pretzels should look golden brown but still feel slightly spring-y to the touch.