In a large mixing bowl, combine the flour, kosher salt, sugar, and instant yeast. Stir until well mixed.
Gradually add the lukewarm water to the dry ingredients, stirring until everything is combined into a sticky dough.
Cover the bowl with a clean kitchen towel or plastic wrap and place it in a warm area. Allow the dough to rise for about 1 hour, or until it has doubled in size.
After the first rise, punch down the dough to release any trapped air. Divide the dough in half and transfer each portion into two greased Pyrex bowls.
Cover the bowls again and let the dough rise for an additional 20 minutes.
Preheat your oven to 425°F (220°C). Once preheated, bake the loaves in the oven for 15 minutes.
After 15 minutes, reduce the oven temperature to 375°F (190°C) and continue baking for another 15-20 minutes, or until the loaves are golden brown and sound hollow when tapped.
Remove the bread from the oven and let it cool slightly in the bowls before carefully transferring the loaves to a wire rack to cool completely.