Soak the rye in advance for several hours until completely cold.
Mix all dry ingredients with warm water.
Let it rest for 15 minutes.
Add levain and mix on slow speed to incorporate.
Switch to a faster speed for 6-8 minutes.
Put to dough in an oiled tub or bowl (covered).
Let it rest for 20 minutes.
Fold twice and then let it rest for another 1.5 to 2 hours; fold the dough very 20 minutes.
Divide into 3 pieces (684g each).
Make tight balls without tearing the skin.
Let them rest for 20 minutes.
Shape into loaf and top with sunflower seeds.
Let it rise for about 4 hours.
Bake at 450F to 470F for 25-30 minutes.