Stir 1 cup warm water (105°F to 110°F), yeast, sugar and salt in an electric mixer fitted with a dough hook. Set aside until yeast has dissolved and mixture bubbles, about 5 minutes. Stir in both flours, set mixer speed to medium and knead with dough hook until dough is smooth and elastic, about 10 minutes. (Or, mix with a wooden spoon and knead by hand.) Transfer dough to an oiled bowl, cover with a clean kitchen towel and set aside in a warm, draft-free spot until doubled in size, about 1 hour.
Preheat oven to 425°F. Oil 2 large baking sheets. Stir baking soda and 2 cups warm water in a bowl until dissolved.
Turn dough out onto a floured work surface; cut into 20 equal-size balls. Working with 1 at a time, roll and stretch each ball to form thin, 12- to 15-inch-long ropes. Twist each into a pretzel shape.
Use a slotted spoon to dip each pretzel into baking soda solution; place on a baking sheet. Reshape as needed. Sprinkle with coarse salt. Bake until browned, about 10 minutes. Remove sheets to a wire rack to cool for 10 minutes; transfer pretzels to rack to cool further.