Crusty Country Sourdough Boule

Steps

1. Feed the starter (Morning of Day 1): mix about 20 g of starter with 40 g flour and 40 g water, cover loosely and leave at about 75°F (24°C). It peaks in 4 to 6 hours, when it has doubled, is domed and full of bubbles, and a spoonful floats in water.
2. Autolyse: about an hour before the starter peaks, stir the flour, whole-wheat flour and all but 15 g of the water in a large bowl until no dry flour remains. Cover and rest 30 to 60 minutes.
3. Mix: add the peaked starter and pinch and squeeze it through the dough for 2 to 3 minutes. Rest 20 minutes, then add the salt with the reserved water and squeeze until fully absorbed. The dough is about 70% hydration and 2% salt, counting the flour and water in the starter.
4. Bulk rise with stretch-and-folds: keep the covered dough at about 75°F (24°C). Every 30 minutes for the first 2 hours, do a set of stretch-and-folds: with wet hands, lift one side of the dough, stretch it up and fold it over, then turn the bowl and repeat on all four sides. Then leave it undisturbed. Bulk takes 4 to 5 hours total and is done when the dough has grown about 50%, looks domed and airy with bubbles on the sides and top, and jiggles when the bowl is shaken.
5. Pre-shape: turn the dough onto an unfloured counter and use a bench scraper to round it into a loose ball. Rest uncovered 20 to 30 minutes.
6. Shape: lightly flour the top, flip it, fold the bottom up, the sides in and the top down, then roll and drag it toward you to build a tight boule (or roll it up into a batard). Place it seam side up in a floured, towel-lined bowl or banneton.
7. Cold proof: cover and refrigerate 12 to 16 hours overnight. It is ready when it has puffed slightly and a floured finger poke springs back slowly, leaving a small dent.
8. Bake (Day 2): place a lidded Dutch oven or heavy covered pot in the oven and preheat to 475°F (245°C) for 45 minutes. Turn the cold dough onto parchment, score the top about 1/2 inch deep with a sharp blade, and lower it into the hot pot.
9. Cover and bake 20 minutes. Uncover, lower the heat to 450°F (230°C) and bake 20 to 25 minutes more, until deep golden brown and the center reads 205 to 210°F (96 to 99°C) on an instant-read thermometer.
10. Cool the loaf on a rack for at least 2 hours before slicing so the crumb sets, then cut into 5 slices.