In the bowl of a stand mixer fitted with the dough hook attachment, combine all of the ingredients for the dough and mix on low until fully combined.
Knead on low for about 5 minutes until the dough is smooth and elastic.
Transfer the dough to an oiled bowl, cover tightly with plastic wrap and place in the fridge overnight (8-24 hours). The dough should roughly double in size.
The next day, add 2 tablespoons of olive oil in the bottom of a 10 inch cast iron skillet. Place the dough on top of the oil and use your hands to gently stretch the dough to the edges of the pan. Cover the dough again and let rest at room temperature for 2-4 hours or until the dough is super light and airy.
Same day option: Instead of placing the dough in the fridge overnight, let rise at room temperature for 1-2 hours or until the dough has doubled in size. Then proceed with the remaining steps. Just limit the second rise to 30-60 minutes.
Preheat the oven to 425°F.
Drizzle the remaining 2 tablespoons of olive oil over the top of the dough. Using your fingers, gently press straight down to create small dimples in the top of the focaccia dough.
Then top with the sundried tomatoes, Kalamata olives, sliced red onion, and goat cheese. Sprinkle the top with flaky sea salt if desired.
Bake at 425°F for 20-30 minutes or until the focaccia is golden brown and the edges are crisp.
Remove from the pan and let cool on a wire rack for at least 10 minutes before slicing. Garnish with fresh oregano if desired.
Focaccia is best eaten the same day but will keep at room temperature for up to 2 days.
Notes
This recipe is designed for a 10 inch cast iron skillet but scales super easily! If you want to make focaccia for a crowd, just double the recipe and bake it in a 9x13 inch cake pan.