Combine flours, water, and starter in a large bowl. Stir until no dry flour remains. Cover and rest 30 minutes.

Sprinkle salt and the 60 g of seeds over the dough. Pinch and fold for about 2 minutes to incorporate evenly.

Cover and let rise at room temperature for 3 to 4 hours, performing 4 sets of stretch and folds during the first 2 hours, one set every 30 minutes.

Shape the dough into a tight boule. Dampen the top and press it firmly into the 2 tbsp mixed seeds. Place seam side up in a floured banneton, cover, and refrigerate 12 to 16 hours.

Preheat a Dutch oven with lid at 500°F for 30 minutes. Turn dough onto parchment, score, lower into the pot, cover, and bake 20 minutes. Uncover, reduce heat to 450°F, and bake 20 to 25 minutes until deep brown.

Cool on a wire rack at least 1 hour, then slice and serve.