In a small bowl, mix the yeast and sugar with warm water. Stir well and let it sit for 5 minutes.
In a large bowl, combine the flours and salt. Mix lightly. Pour in the yeast mixture and lukewarm water. Stir with a wooden spoon until a uniform dough is formed. The dough will be sticky, which is normal. Cover and let it rise for 30 minutes.
Preheat the oven to 430 F (220 C). Line a parchment paper, and transfer the dough onto it. Shape it into a round loaf and create a hole in the center. Place the small bowl inside the hole. Transfer everything, with the parchment paper, into the cast iron pot and cover it.
Using a sharp knife, cut off the narrow part of the garlic head to create a flat surface. Wrap it in tin foil and place on top of the pot. Transfer to the oven and bake for 35 minutes.
Uncover and bake for another 10-15 minutes until the bread turns golden. Remove from the oven and let it cool slightly.
Remove the bread from the pot. In a small bowl, combine the softened butter, finely chopped herbs, and salt. Unwrap the garlic cloves, squeeze them into the bowl and mix well.