In a large bowl, stir together the starter, water, yeast, sugar and salt. Stir in the flour 1 cup at a time until a shaggy dough starts to come together. Dump the dough onto a well-floured surface and knead for several minutes, sprinkling with more flour as needed, until the dough is smooth and elastic.
With a stand mixer:
In the bowl of a stand mixer fitted with a dough hook, combine the starter, water, yeast, sugar and salt, stirring together until just combined. While the machine is running, slowly add the flour 1 cup at a time, mixing until the dough is no longer sticky and pulls away from the sides of the bowl.
For both methods:
Allow the dough to rise in a covered bowl until it has doubled in size, about 60-90 minutes (depending on how warm your rising location is).
Once the dough has risen, pour the dough onto a lightly floured surface - it will deflate somewhat. Shape the dough into a loaf - I like to shape mine into a round loaf by pulling the sides under, almost like a bubble gum bubble, though you could also shape it into an oval if you prefer. Place the loaf onto a parchment-lined baking sheet, cover with a tea towel and allow to rise until very puffy, about 45 minutes to 1 hour.
Near the end of the second rise, preheat the oven to 425 degrees.
Just before placing the loaf in the oven, spray it with lukewarm water. Then, using a sharp knife - a large, serrated bread knife works well for this - make two diagonal slashes in the top of the loaf.
Bake for 25 to 30 minutes, or until very deep golden brown. Transfer to a rack to cool for at least 15 minutes before slicing and serving.
Notes
Only have active dry yeast available? Not a problem. Simply combine the yeast, lukewarm water, and sugar and allow to sit for about 5 minutes, or until the yeast is foamy (read: activated). Then continue with the recipe as written.