In a large mixing bowl, combine warm water, sugar, and yeast. Let sit for 5 minutes until foamy.
Add flour, salt, and melted butter to the yeast mixture. Mix until a dough forms.
Knead the dough on a floured surface for about 5-7 minutes until smooth and elastic.
Place dough in a greased bowl, cover, and let rise in a warm place for about 1 hour or until doubled in size.
Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a large pot, bring water and baking soda to a boil.
Divide the dough into 8 equal pieces and shape each piece into a ball.
Boil each dough ball in the baking soda bath for 30 seconds on each side. Remove with a slotted spoon and place on the prepared baking sheet.
Sprinkle each bun with coarse sea salt.
Bake in the preheated oven for 12-15 minutes or until golden brown.
Let cool on a wire rack before serving.