In a large non-metal bowl, stir together the sourdough starter, 1 cup water and 1¾ cups flour. Let it sit for 1 hour
Add the remaining 4½ cups flour, 1¾ cups water and the salt.
Mix in a stand mixer with the dough hook for 2 to 3 minutes, or knead on a lightly floured surface for 7 to 8 minutes. The dough will feel soft and a little sticky.
Place the dough in an glass bowl and let it rise until doubled, about 10 to 12 hours.
Day 2
Dust a 10-inch cast iron skillet with flour and place the dough in the skillet.
Bake at 400°F for 35 to 40 minutes.
Cool on a rack for at least 1 hour before slicing.
Notes
TIP: if it is a warm day, place the bowl of dough in your warm car and it will rise beautifully)