In a small bowl, combine warm water with sugar and yeast. Let sit for 10 minutes. In a large bowl, combine flour and salt. Pour in yeast mixture and melted butter. Mix until a dough forms.
Knead dough on a floured surface until smooth. Place dough into a large bowl, turning to coat. Cover and let rise for 1-2 hours, or until doubled in size.
Preheat oven to 400 F. Deflate dough and divide into 8-10 pieces. Twist each into a pretzel.
In a large saucepan over medium heat, bring water and baking soda to a boil. Boil each pretzel for 30-40 seconds. Remove from water with a slotted spoon. Place onto a large baking sheet. Sprinkle with salt. Bake for 10-12 minutes.
