In a large mixing bowl, whisk together flour, salt and yeast. Add water and stir until a shaggy mixture forms (mixture will be loose and sticky; this is what you want). Cover bowl with plastic wrap and set aside for 12 - 18 hours (up to 24). Overnight works great.
Preheat oven to 450. Place a cast iron dutch oven with a lid in the oven and heat the pot for 30 minutes. Meanwhile, pour the risen dough onto a heavily floured surface (mixture will be sticky) and lightly shape into a round loaf.
Remove hot pot from the oven and carefully set in the dough. Cover and return to oven for 30 minutes. Then, remove the lid and bake an additional 10-15 minutes. Carefully remove bread from oven and from pot and place on a cooling rack.