In a large bowl combine the starter, water, and 3 cups of flour. Beat vigorously for 1 minute.

Cover, and let rest at room temperature for 4 hours.

Refrigerate overnight, for about 12 hours.

After refrigeration, add the remaining 2 cups of flour, sugar, and kosher salt.

Knead to form a smooth dough. Knead either by hand or with a dough hook attached to a mixer.

Allow the dough to rise in a covered bowl until it's light and airy, with visible gas bubbles. Depending on how active your starter is this may take up to 5 hours, or even longer. For best results, gently deflate the dough once an hour by turning it out onto a lightly floured or lightly greased work surface; stretching and folding the edges into the center; turning it over, then returning it to the bowl. Adding these folds will help strengthen the dough’s structure, and allow you to feel how it’s progressing over time. 

Note: sourdough bread (especially sourdough without added yeast) can be finicky and may not go exactly to the written plan. Please allow yourself to go with the flow, and not treat this as an exact to-the-minute process.

When the dough is ready, transfer the dough to a lightly floured or lightly greased work surface and gently divide the dough in half.

Gently shape the dough into two oval loaves, and place them on a lightly greased or parchment-lined baking sheet. Cover with lightly greased plastic wrap and let rise until very puffy, about 2 to 4 hours. This step could take longer but give them sufficient time to become noticeably puffy. Don't worry if the loaves spread more than they rise, they'll pick up once they hit the oven's heat.

Towards the end of the rising time, preheat the oven to 425°F.

Spray the loaves with lukewarm water.

Slash the loaves. If you've made round loaves, try one slash across the center, and a curved slash on each side of it; or slash in the pattern of your choice. For oval loaves, two diagonal slashes are fine. Make the slashes fairly deep, a serrated bread knife works well here.

Bake the bread for 25 to 30 minutes, until it's a very deep golden brown.

Remove it from the oven, and cool on a rack.

Store bread, loosely wrapped in plastic, for several days at room temperature or freeze for longer storage.