In a large bowl add starter, water, egg, oil, maple syrup, and vinegar. Whisk well.
Add remaining dry ingredients. Mix until a dough begins to form.
Knead the dough, adding flour as needed, to form a smooth but still slightly tacky round of dough.
Place in a greased bowl or in a greased parchment paper-lined pan. Cover and let rise overnight or at least 6 hours.
Place the dough in the refrigerator for 4 hours.
Preheat oven to 425°F. Place a cast iron skillet or dutch oven into the oven while it preheats, for at least 30 minutes.
Remove the dough from the refrigerator and knead slightly to re-form a nice round of dough. Optionally, score the dough with any design of your choosing. Allow the dough to rest at room temperature while the oven and pan preheat.
After 30 minutes of resting time, place the dough into a greased parchment paper-lined dutch oven or cast iron skillet. If using a dutch oven, place a few ice cubes on the outside of the parchment, but on the inside of the pan before placing the lid and on and placing into the oven. If using a cast iron or other oven-safe skillet, place a pan of water on the bottom rack of the oven right after place the bread on the middle rack. Keep the oven door closed the entire time to ensure proper steaming.
Bake for 35-40 minutes or until the bread has formed a nice golden crust, is firm and sounds hollow when you tap on the bottom.
Let the bread cool completely before slicing for best results. Slicing too soon can result in a gummy or dense bread.
Slice and enjoy!