1. One day before baking, in a large bowl, stir together sourdough starter, water and honey with a fork or spatula until starter is evenly mixed into the water; set aside for 5 minutes. Stir in flour, 18 grams salt and yeast with a wooden spoon. Turn dough out onto a lightly floured surface. Knead for 8 to 10 minutes or until smooth and elastic.
2. In a medium bowl, place 2 tablespoons olive oil; add dough. Cover with plastic wrap and let rest for 1 hour.
3. Leaving dough in the bowl, with wet hands lift one side of dough and pull it up and over toward the center. Repeat 3 more times. Let rest, uncovered, for 1 hour.
4. In an 18×13-inch rimmed baking pan, place 2 tablespoons olive oil. Add dough to baking pan; turn dough over to coat both sides. Gently stretch dough to the corners and edges of the pan. Spray one side of a large piece of plastic wrap with nonstick cooking spray; place over dough in pan to loosely cover. Place in refrigerator and let rest for 12 to 24 hours.
5. To bake, remove dough from refrigerator; uncover dough and let stand at room temperature for 1 hour. Use fingertips to poke small indentations all over the top of the dough. Drizzle with remaining 2 tablespoons olive oil.
6. Press desired toppings into top of dough. Bake for 25 to 30 minutes or until crispy and golden brown.
7. Slightly cool focaccia in baking pan on a wire rack. Drizzle with additional olive oil and sprinkle with additional flaky sea salt, if desired.

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*Note: see Strawberry 'Donut' Sourdough Focaccia, Apple-Shallot & Gruyère Sourdough Focaccia, and Garlic-Tomato Jam Sourdough Focaccia for toppings.