Dissolve yeast and sugar in warm water in a large bowl, and let stand for 5 minutes.
Lightly spoon flour into dry measuring cups; level with a knife. Add 3 cups flour and 1 teaspoon salt to yeast mixture; stir until a soft dough forms. Turn dough out onto a lightly floured surface; knead until smooth and elastic (about 8 minutes). Add enough of remaining flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel slightly sticky).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 40 minutes or until doubled in size. (Gently press two fingers into dough. If indentation remains, the dough has risen enough.) Punch dough down; cover and let rest 5 minutes.
Preheat oven to 425°.
Divide dough into 12 equal portions. Working with one portion at a time (cover remaining dough to prevent drying), roll each portion into an 18-inch-long rope with tapered ends. Cross one end of rope over the other to form a circle, leaving about 4 inches at end of each rope. Twist the rope at the base of the circle. Fold the ends over the circle and into a traditional pretzel shape, pinching gently to seal. Place pretzels on a baking sheet lightly coated with cooking spray. Cover and let rise 10 minutes (pretzels will rise only slightly).
Combine 6 cups water and baking soda in a nonaluminum Dutch oven. Bring to a boil; reduce heat, and simmer. Gently lower 1 pretzel into simmering water mixture; cook 15 seconds. Turn pretzel with a slotted spatula; cook an additional 15 seconds. Transfer pretzel to a wire rack coated with cooking spray. Repeat procedure with remaining pretzels.
Place pretzels on a baking sheet sprinkled with cornmeal. Combine 1 teaspoon water and egg in a small bowl, stirring with a fork until smooth. Brush a thin layer of egg mixture over pretzels; sprinkle with kosher salt. Bake at 425° for 12 minutes or until pretzels are deep golden brown. Transfer to a wire rack to cool.
We love these pretzels. They take some time to make but the preparation is easy. Ours are a little thinner than the ones in the picture. I'm not sure how to "fluff" them up any more as we didn't shortcut either of the risings. They are fun to shape with kids. We will definitely be making these again.