Took me more bakes than I care to admit to finally get this!

310g white bread flour

15g whole wheat flour

3g diastatic malt powder

7g salt

255g water

65g bread flour levain (100% hydration)

Make 2:1:1 levain and autolyse flour, malt, and water in warm proofing box until levain is tripled in size (4-5 hours)

Thoroughly mix levain into dough, rubaud about 3 minutes, then rest + 30 minutes

Add salt, another vigorous 3 minute mix + 30 minutes

Strong stretch and fold + 30 minutes

Laminate + 30 minutes

Coil fold + 30 minutes (x3)

Bulk ferment 5-6 more hours at 78° dough temp until about a 50% rise (I use an aliquot jar)

Gentle pre-shape + 20 minutes

Shape into batard, carefully stitched

Straight into refrigerator for a 24 hour cold retard

Dutch oven fully preheated to 500°

Score and bake covered for 15 minutes at 475°

Finish bake uncovered for ~20 minutes

Many, many failed loaves, but worth the patience and practice!