most of a head of garlic (about 10 cloves)
1/2 c olive oil
3 T fresh rosemary
2 c sourdough starter
1 c warm water
1 t yeast
1 c semolina + some for sprinkling
2 c + 2.5 c bread flour
1 T kosher salt + some for sprinkling
Peel garlic cloves and crush with the flat blade of a large knife instead of chopping. Put the cloves in a little bowl with oil and rosemary, and let sit while the sponge rises.
To make that sponge, combine starter, water, yeast, semolina, and 2 c flour in a large bowl, and stir vigorously. Cover tightly with plastic wrap and put in a warmish place (eg oven with the pilot light on) until doubled in size (I got home 6 hr later and it looked great).
Stir to deflate, then thoroughly stir in the by-now-delicious-smelling oil and its contents. Stir in the salt and remaining 2.5 c flour, and knead for a good while to make a sticky, rope-y dough. Good ways to knead this are to pull fistfuls of dough in circular motions around the bowl, or to pull fistfuls up out of the bowl; both methods should result in visibly nice stretchy glutenous structures. As always with bread, the actual feel of your dough matters more than what you've added; if your dough is stiff enough that you could knead it on a board if you wanted to, squeeze in a few tablespoons (even half a cup) of milk and knead until the texture seems right. Cover again and put back in your warm place until doubled (about 2 hr).
Prepare a baking sheet or two by lining with parchment and sprinkling well with semolina. Punch the dough to deflate and split in half. With each half, scrape it out of the bowl and form into a smooth ball by holding it in the air between your hands and quickly and repeatedly pulling the bottom surface up toward the top. Place each ball top-seam-side down on the semolina, and sprinkle with more semolina and a bit of salt. Place the pan(s) in the oven above a pan of boiling water and let rise until doubled (about 1.5 hr).
Take the loaves out of the oven, move the water pan to the top position and the free rack to the lowest position, and start preheating to 450F. Put the loaves in on the lower rack when it's fully preheated, and turn the heat down to 400F. Bake for 35 min until golden brown all over and kinda sorta hollow-sounding when tapped on the bottom. In case they're not cooked through optimally, and as a generally good practice, cool completely (overnight, in paper bags) before slicing. This makes a soft, pungent, and quite tasty bread.