Combine flour, salt, and yeast in your tub. Whisk. Add 1½ cups or 350g warm water. With a flexible spatula, stir until all of the flour has been incorporated: peek through the bottom of the tub to check for any streaks of dry flour.
Cover and let rise. When the dough reaches about 3× its original height (between the ridge and 2 quart mark) poke the spatula into the center to deflate, then run it along the tub’s wall to pull the dough into a rough ball.
Cover and let rise again. We call this 2nd rise the proof. Meanwhile, preheat the oven to 450°F with an 8" cast iron skillet on a rack at or just above center. When the dough again reaches approximately 3× its original height, it’s ready to bake.
Retrieve the hot skillet and quickly close the oven door. Add a little fat to the skillet and swirl to cover its floor, then set the skillet on a hot pad. Tip the tub and run the spatula along its wall and floor to transfer the dough into the skillet without deflating.
Reduce the oven temperature to 400°F. Place the skillet in the oven and bake 45–50 min. Then, with a hot pad protecting each hand, retrieve the skillet and tip it to set the loaf onto the hot pad in your other hand. Tap the bottom crust to check for doneness: if it’s soft, bake the loaf directly on the oven rack for a few more minutes. Cool on a rack.