Combine all seeds in a bowl, pour boiling water over, and let soak for at least 1 hour.
Mix both flours, starter, and water in a large bowl until no dry flour remains.
Cover and let rest for 30 minutes (autolyse).
Drain any excess water from seeds.
Add salt and soaked seeds to dough, squeezing and folding with wet hands until incorporated.
Cover and let rest for 30 minutes.
Perform a series of 4 stretch and folds, spaced 30 minutes apart: wet your hand, grab one side of dough, stretch up, and fold over itself, rotate bowl 90 degrees, repeat.
After final fold, cover and let bulk ferment for 3-5 hours until increased by 50% and jiggly.
Turn out onto a floured surface and shape into a tight round.
Place seam-side up in a floured banneton or bowl lined with a tea towel.
Cover and refrigerate for 8-12 hours.
Heat oven to 240°C with a Dutch oven inside for 30 minutes.
Turn dough out onto parchment, score the top with a sharp knife.
Carefully place in hot Dutch oven, cover with lid.
Bake covered for 25 minutes, then remove lid and bake 20-25 minutes more until deep brown.
Cool on a wire rack for at least 1 hour before slicing.