Preheat the oven to 250. In a small oven safe dish combine peeled garlic cloves and enough olive oil to cover them. Bake until garlic is golden brown and completely softened, 1-1 1/2 hours. Remove and allow to cool. (This step can be done a few days beforehand).
Make the bread dough. Combine flour, yeast, salt and chopped sage in the bowl of a stand mixer. Add the water and olive oil from the roasted garlic (you can use some regular olive oil if you don't have quite enough) and roughly mix with a spoon into a shaggy dough.
Fit the mixer with the dough hook and knead dough on medium until tender and stretchy, 5 minutes. Alternatively, you can knead the dough by hand.
Coat the bottom and sides of a large bowl with olive oil. Transfer dough to this bowl, cover and allow to rise until doubled in size, 1 1/2 hours.
After the first rise, turn the dough out onto a floured work surface. Roll out into a rough rectangle and evenly distribute the cloves of roasted garlic on top. Roll the dough back up and knead a few times to ensure the garlic is evenly distributed, then roll into a round loaf shape.
Lightly flour a cast iron skillet and place the bread dough in it. Cover and allow to rise again, 1 hour.
When dough is almost risen, preheat oven to 425. Bake bread right in the cast iron skillet until browned and it sounds hollow when knocked, 45-50 minutes. Allow to cool before slicing.