In a large bowl, combine warm water, sugar, and yeast. Let sit for 5–10 minutes until foamy.
Add flour and salt to the yeast mixture. Stir until a dough forms, then knead on a floured surface for 5–7 minutes until smooth and elastic. Place in a greased bowl, cover, and let rise for 1 hour or until doubled in size.
Preheat oven to 450°F (230°C). Bring 6 cups of water to a boil in a large pot and stir in baking soda (be careful—it will bubble vigorously).
Punch down the risen dough and divide into 8 equal pieces. Roll each into a rope about 20 inches long, then form into a pretzel shape by crossing the ends over twice and pressing into the bottom.
Carefully lower each pretzel into the boiling baking soda solution for 30 seconds. Use a slotted spoon to transfer them back to a parchment-lined baking sheet.
Brush each pretzel with beaten egg yolk and sprinkle generously with coarse sea salt.
Bake for 12–15 minutes, until deep golden brown. Cool slightly before serving.
Notes
These pretzels are best served warm with mustard or cheese dip.