In a bowl of a stand mixer fitted with a dough hook combine the water and yeast. Stir to dissolve. Add 1 cup of whole wheat flour and 1/2 cup of all-purpose flour. Using the paddle attachment, mix on low speed for 3 minutes. Cover with a towel and let rise for 30 minutes.
Prepare two 6-inch cast-iron (or any oven-safe) skillets by rubbing generously with olive oil.
Stir in olive oil, salt and 2 tablespoons of the rosemary to the dough. Add remaining 1 cup of whole wheat flour and 3/4 cup of all-purpose flour. Switch to dough hook attachment. Mix on low speed for 3-4 minutes. Add more flour if the dough is still very sticky, one tablespoon at a time; but it should be soft and not too stiff and wrapped around the dough hook.
Turn dough onto a lightly floured surface. Gently knead the dough into a ball, then divide in 2 equal pieces. Knead each piece into a ball and place in the prepared skillets. Press down on them to fill the space. Cover with a towel and let rise for about 30 minutes.
Preheat the oven to 400°F.
Using a pastry brush, gently glaze each dough with olive oil and then sprinkle the remaining rosemary over the top. Slice each loaf in a diagonal pattern with a sharp serrated knife and sprinkle with some sea salt flakes.
Bake in the oven for about 25 minutes and the bread is golden brown. Once the bread comes out of the oven, brush with more olive oil and let cool.