In a large mixing bowl, combine the sourdough discard, warm water, and sugar. Stir until the discard is mostly dissolved. If using active dry yeast, whisk it into the water first and let it sit for 5 minutes to bloom before adding the discard and flour.

Add the all-purpose flour and fine sea salt to the bowl. Mix with a sturdy spoon or spatula until a shaggy, sticky dough forms; ensure no dry patches of flour remain.

Cover the bowl with a damp kitchen towel or plastic wrap. Let the dough rise in a warm, draft-free spot for 4-12 hours until bubbly and more than double in size.

Generously coat a 9x13 inch baking pan with 1/4 cup of olive oil, covering the entire bottom and up the sides.

Gently scrape the sticky, risen dough into the prepared pan. Use oiled hands or a spatula to stretch and press the dough toward the edges of the pan.

Cover the pan loosely and let it rest for 30-60 minutes for a second rise. Meanwhile, preheat your oven to 425°F (220°C).

Once the dough has rested and looks puffy, uncover it. With oiled fingers, press straight down into the dough to create deep wells and dimples all over the surface.

Drizzle the top generously with more olive oil, letting it pool in the dimples. Sprinkle evenly with coarse sea salt and add any chosen toppings.

Bake for 22-28 minutes, until the top is deeply golden brown and edges are crisp. The internal temperature should read around 200°F.

Remove the focaccia from the oven and carefully transfer it from the pan to a wire cooling rack. Let it cool for at least 15 minutes before slicing and serving.