12 hours before you want to bake your sourdough, mix together the sourdough starter, warm water, and honey together in a large bowl.
Add in the flour, salt, and garlic powder and mix until combined.
Cover the dough and allow it to rest for 30 minutes. This allows time for the flour to hydrate and the gluten begin to activate.
With wet hands, pull the edges of the dough upwards until they won't stretch anymore then fold over onto itself. Repeat on all four sides of the dough. (see the video for a demonstration).
Cover the dough with lightly oiled plastic wrap and place it in a warm place (65ºF-80ºF) for 12 hours (overnight). Keep in mind that if your room is colder or hotter, the bread may rise slower or faster.
The next morning, cover your sheet pan in a thin even layer of olive oil.
Transfer the dough to the sheet pan and cover it again with plastic wrap to rise again for 1-2 hours or until very puffy and bubbly. The dough will spread as it rises.
Preheat your oven to 425ºF.
Dimple the top of the dough with oiled fingers. Drizzle the top of the dough with more olive oil, flake salt, and chopped rosemary (or toppings of your choice).
Bake your focaccia for 20-25 minutes or until golden brown.
Remove the bread from the pan after it's done baking and let it cool on a wire rack before cutting into it.