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.