Mix water, sourdough starter, salt, and 1 tbsp olive oil together gently in a large bowl.
Add one cup of flour and mix to incorporate.Then, add the rest of the flour and mix until combined. (The dough will be very wet but should still resemble a dough ball in the bowl.)
Oil a large bowl with 1 tbsp olive oil. Transfer the dough to the oiled bowl. If necessary, oil your hands slightly so the dough will not stick as much.
Cover the dough with plastic wrap and set a timer for 30 minutes.
After 30 minutes, wet your hands and grab a fist full of the dough. Stretch the dough up towards you, then fold it over the top of the dough ball. Turn the bowl and repeat this three more times until you have stretched and folded the whole ball of dough.
Cover the dough and again set a timer for 30 minutes. After 30 minutes, repeat the stretch and fold in the previous step.
Cover the dough and let it sit at room temperature for 12–24 hours. If it is warmer in your house, you can place the dough in the fridge for this part.
Once the dough has fermented for 12–24 hours it will have doubled in size and grown more bubbly. At this point, pour 3-4 tbsp of olive oil in an 11” cast iron skillet. Transfer the dough into the skillet and cover.
Let the dough rise for 2-3 hours or until it fills the bottom of the cast iron pan.
Preheat the oven to 400°F.
After the dough has risen a second time, pour 2 tbsp olive oil evenly across the top. Push all of your fingers into the dough to dimple it, and move your hands slightly while dimpling the dough so that the olive oil will be well dispersed. Repeat this several times across all of the dough.
Sprinkle some flaky sea salt on the dough and your preferred amount of rosemary.
Bake sourdough focaccia for 30 minutes or until it starts to turn golden brown.
Take the bread out of the oven, and add sundried tomatoes. Add a few spoonfuls of the oil from the tomatoes for extra flavor.
Place the bread back in the oven for another 5–7 minutes or until it is fully golden brown on top.
Let the bread rest for 10 minutes before cutting.
Add more flaky sea salt and oil from the sun dried tomatoes and enjoy!