In a mixing bowl combine the sourdough starter and water.
Pour into a large mixing bowl or the bowl of a stand mixer.
Add in the flour, sea salt and honey. Mix on medium speed for 5-7 minutes with the hook attachment, until a sticky dough is formed. (or by hand for 10-12 minutes)
Transfer the dough to another bowl that has been greased. Cover and let rise in a warm place for 1 hour.
After the hour, remove the cover and fold the dough over 3-4 times, scraping down the sides and folding in towards the center.
Drizzle about 2 tablespoons of olive oil into the bottom of a half sheet baking pan (13" x 18").
Place dough onto the pan and turn to coat in oil. Stretch the dough out to the edges of the pan. Let rest 10 minutes and stretch again.
Cover the dough with plastic wrap that has been sprayed with cooking spray and place in the refrigerator for 10-12 hours.
Remove from the refrigerator 1-2 hours before baking and allow to come to room temperature.
Preheat the oven to 425º F
Drizzle 2 tablespoons of olive oil over the top of the focaccia and use your fingers to poke dimples all over the top of the dough.
Sprinkle with sea salt, garlic powder and fresh rosemary.
Bake for 20-25 minutes, until golden brown on top.
Remove from the oven and allow to rest for 10 minutes before enjoying.