In a medium bowl combine the water, flour and yeast. Cover the bowl with plastic wrap and let it sit at room temperature for 1 ½ to 2 hours. Then transfer the biga to the refrigerator overnight for 12 to 48 hours.
Remove the biga from the refrigerator. It will look fully hydrated, expanded and should be a little bubbly.
Into a large bowl add the water, all of the biga, 3 tablespoons of oil and stir to combine. Add the flour, salt, yeast and sun dried tomatoes, stirring with a wooden spoon until the flour is hydrated. You will have a sticky, bumpy, shaggy but homogeneous dough. Cover with plastic wrap and set it in a warm corner of your kitchen for 30 minutes.
Wet your hands to stretch and fold the dough. To do this, scoop your fingers down the sides of the bowl so they meet under the dough in the middle. Lift the dough up above the bowl. Lift and fold the dough over itself 3 times. Coming from different edges of the dough each time. Cover with plastic wrap. Repeat this process every 30 minutes for the next 2 ½ hours.
Place a sheet of parchment paper in the bottom of a 9x13 cake pan. Generously coat the parchment paper with ⅓ cup oil. Place the dough on the baking sheet or pan, and turn it over gently to coat.
Using the tips of your fingers gently insert into the dough in multiple places, creating dimples and stretching the dough gently toward the edges of the pan. Do this 3 to 4 times over the next 1 to 1 ½ hours.
Preheat the oven to 450°F.
Before the final dimple, drizzle 3 tablespoons of oil over the dough and sprinkle with kosher salt.
Place the pan in the oven and bake for 28-35 minutes. When it’s done it should be golden brown with darker brown bubbles. Remove from the oven.
Give it about 5 minutes to cool, then transfer it to a cutting board. It should be crisp on the outside, tender, slightly chewy and full of air pockets on the outside.