10:00 PM: In a clean glass jar, combine your 15g of starter culture with 50g of water and whisk together thoroughly. Add the 75g of all-purpose flour and knead briefly into a tight, firm ball. Cover loosely and let it ferment at room temperature 74–78°F (23–26°C) overnight for 8 to 10 hours until it at least triples in volume and peaks.

8:00 AM – The Autolyse: In a large bowl, whisk together the 400g of bread flour and 70g of earthy buckwheat flour. Pour in 376g of water and stir until a rough, wet dough builds with no dry flour streaks. Cover and let autolyse undisturbed for 1 hour to fully hydrate the ancient grains.

9:00 AM: Add 140g of your mature stiff starter and 9g of salt directly to the autolysed dough. Knead by hand for 3 to 5 minutes, dimpling and pinching the dough repeatedly until the firm starter breaks down completely and integrates smoothly into the wet dough.

Cover the bowl and let bulk ferment for 3 hours at a warm room temperature of 76–80°F (24–27°C).

During the first 2 hours of bulk fermentation, perform 4 separate rounds of structural stretch-and-folds every 30 minutes. Dip your hands in water, pull the edges of the dough up high, and fold them over the center to build tension. By the final rest, the dough will look smooth, strong, and carry visible air pockets.

12:00 PM – The Couronne Shape: Generously dust your couronne proofing basket with flour. (If you do not have a specialized ring basket, place a clean towel inside a large standard bowl, dust it heavily with flour, and center an inverted, well-floured small glass bowl right in the middle).

Tip the puffy dough out onto a lightly floured surface and gently shape it into a smooth, round boule.

Flour your hands well. Plunge your index finger straight down through the exact center of the dough ball until you hit the counter, then gently rotate your hands inside the gap, pulling outward to widen it into a large, uniform doughnut ring.

Flip the shaped ring upside down into your prepared proofing basket so the smooth top rests against the bottom. Cover loosely and let proof for 2 hours at room temperature until it expands and feels light to the touch.

1:30 PM: Position a heavy baking stone or baking sheet on the middle rack of your oven and preheat to 450°F (230°C). Place an empty cast iron skillet onto the bottom rack to serve as your steam generator.

2:00 PM: Flip the proofed crown loaf gently onto a sheet of parchment paper. Using a sharp razor blade or lame, score a series of clean, overlapping diagonal slashes all the way around the ring curve.

Slide the loaf (with the parchment) directly onto the hot baking stone. Immediately pour 1 cup of boiling water into the hot cast iron skillet below to create a burst of steam, shut the oven door instantly, and bake at 450°F (230°C) with steam for exactly 20 minutes.

Carefully remove the steam tray, lower the oven temperature to 425°F (218°C), and continue baking dry for an additional 15 minutes until the buckwheat crust turns a rich, dark espresso color. Let cool completely on a wire rack before slicing.