In a small bowl, combine the warm water and active dry yeast. Let it sit for about 5 minutes until it becomes frothy.
In a large mixing bowl, whisk together the whole wheat flour, all-purpose flour, and salt.
Once the yeast mixture is frothy, pour it into the bowl with the dry ingredients. Add the sunflower seeds and flax seeds. Mix until a shaggy dough forms.
Transfer the dough onto a lightly floured surface and knead for about 8-10 minutes until smooth and elastic.
Place the dough in a greased bowl and cover it with a kitchen towel. Let it rise in a warm place for about 1-2 hours or until it has doubled in size.
Once risen, punch down the dough to release any air bubbles. Shape it into a round loaf and place it in the preheated cast iron skillet.
Cover the skillet with the kitchen towel again and let the dough rise for about 30-45 minutes until it puffs up.
While the dough is rising, preheat your oven to 375°F (190°C).
Once the second rise is complete, bake the bread in the preheated oven for 30-35 minutes or until the top is golden brown.
Remove the bread from the oven and let it cool in the skillet for about 10 minutes before transferring it to a wire rack.
