The night before you're going to bake, make the levain: Weigh the spelt flour, or measure it by gently spooning it into a measuring cup and sweeping off the excess. Mix the spelt flour, water, and starter together, cover, and set aside at room temperature for 12 hours, or overnight. At this time the levain should be expanded and very bubbly, but not yet starting to fall., The next day, weigh the flours, or measure them by gently spooning them into a measuring cup and sweeping off the excess. Combine the flours with all the levain, and the remaining dough ingredients., Mix and knead everything together — by hand, mixer, or bread machine set on the dough cycle — until you have a soft, smooth, elastic dough, incorporating only as much of the remaining 1/2 cup of all-purpose flour as you need to keep the dough from sticking; it will quickly become smooth and elastic., Let the dough rise, covered, for about 1 hour. It won't double in that time, but it will start to get puffy. Meanwhile, grease a 9" x 5" loaf pan. , After an hour, remove the dough from the bowl and form it into a 9" log. Place the loaf in the pan, cover it, and let it rise for 1 to 1 1/2 hours., About 30 minutes before you're ready to bake, preheat your oven to 425°F. Prepare your oven for steaming by placing an oven-safe pan on the bottom rack before preheating. As the oven is preheating, heat a small pan of water on the stove until it comes to a simmer. , Slash the loaf lengthwise down the center; dusting the loaf lightly with flour will help you make a neater slash and gives the finished loaf a nice artisan look., As the loaf goes into the oven, pour a small amount (about 1/2 cup) of the hot water into the pan in the oven to create a burst of steam (we recommend using oven mitts for this job). Immediately shut the oven door, bake the bread for 10 minutes at 425°F, then reduce the oven temperature to 400°F, and bake for 30 to 35 minutes longer, tenting the loaf with foil for the final 15 to 20 minutes of baking to prevent over-browning. Bake until the loaf is nicely golden; a digital thermometer inserted into the center of the loaf should read 190°F. , Remove the bread from the oven, turn it out of the pan immediately, and cool it thoroughly before slicing., Store bread at room temperature, well wrapped, for several days. Freeze for longer storage.