Preheat oven to 400°F.
Mix water and yeast, allow to sit ≈5 minutes or until foamy. Mix in remaining ingredients (except reserved butter), and knead until combined. If too sticky, add additional flour.
Divide into 4 pieces, roll into balls, and space 2 inches apart in a cast iron skillet or baking pan. Allow to rise 20 minutes or until doubled in size.
Brush with reserved butter. Bake until golden brown, about 25 minutes. Brush with butter again, sprinkle with kosher salt, and serve.