Add the sourdough starter and salt to a large bowl.
Pour in the lukewarm water and mix with a rubber spatula, until the starter has fully broken apart and disenegrated in the water.
Sprinkle in the flour and mix with the spatula. The dough will be shaggy and a bit lumpy, that's okay.
Add in 1 tablespoon of olive oil around the sides of the dough, work it in slowly a few times. The oil will still spill on the sides, this is also okay.
Cover and let the dough rise for 8 to 12 hours, or overnight.
Add the other 1 tablespoon of olive oil on the bottom of a deep baking sheet, then add the dough using a spatula.
Add a bit more olive oil to your fingers, then press into the dough to make divets. The olive oil is to prevent the dough from sticking to your hands.
Cover with a towel and let it rise again, this time for 6 to 8 hours.
Preheat the oven to 450 degrees. Sprinkle the top of the risen sourdough focaccia with flaky sea salt, and any other desired toppings.
Bake in the oven for 25 to 30 minutes, or until the top becomes golden brown.