By Hand: Stir the yeast into the water in a large mixing bowl; let stand until creamy, about 10 minutes. Stir in the milk and oil. Combine the rosemary, salt, and flour and stir into the yeast mixture in 3 or 4 additions. Stir until the dough comes together. Knead on a floured surface until velvety, elastic, and smooth, 8 to 10 minutes. It should be somewhat moist and blistered.
By Mixer: This recipe is slightly large for the mixer, so that you'll have to stop and push the dough down frequently while the mixer is kneading it. Stir the yeast into the water in a mixer bowl; let stand until creamy, about 10 minutes. Stir in the milk and oil with the paddle. Combine the rosemary, salt, and flour and add to the yeast mixture. Mix until the flour is absorbed, 1 to 2 minutes. Change to the dough hook and knead on medium speed until velvety, elastic, smooth, and somewhat moist, about 3 minutes. Finish kneading briefly by hand on a lightly floured surface.
First Rise: Place the dough in an oiled bowl, cover tightly with plastic wrap, and let rise until doubled, about 1 1/2 hours.
Shaping and Second Rise: Gently punch the dough down on a lightly floured surface, but don't knead it. Cut the dough in half and shape each half into a round ball. Place the loaves on a lightly floured peel or lightly oiled baking sheet, cover with a towel, and let rise 45 to 55 minutes (but not until truly doubled).
Heat oven to 450 degrees F. If you are using a baking stone, turn the oven on 30 minutes before baking and sprinkle the stone with cornmeal just before sliding the loaves onto it. Just before you put the loaves in the oven, slash the top of each loaf in an asterisk with a razor blade and sprinkle half the sea salt into the cuts of each loaf. Bake 10 minutes, spraying 3 times with water. Reduce the heat to 400 degrees F and bake 30 to 35 minutes longer. Cool completely on racks.