In a large bowl, gently whisk together the warm water, sugar, and yeast to combine. Let rest for 5 to 10 minutes, until the mixture is foamy and bubbly.

Add in the flour, 2 tablespoons olive oil, and 1 teaspoon kosher salt to the yeast mixture. Use a rubber spatula to mix the mixture together until well combined. Continue stirring and folding the dough over on itself for about a minute; the dough will be very sticky.

Cover the bowl with plastic wrap or a clean kitchen towel and let the dough rise at room temperature until it has doubled in size; about an hour.

Use your hands to grease the bottoms and sides of a 9x13 inch baking pan with 2 tablespoons of olive oil. Then, use your greased hands to transfer the dough to the baking pan, spreading the dough so it mostly covers the bottom of the pan.

Cover the pan with plastic wrap or a clean kitchen towel and let the dough rise for about 45 minutes. During last few minutes of rising, preheat oven to 425 degrees.

After the dough has risen, drizzle remaining 2 tablespoons of olive oil over the top of the dough. Use oiled fingers to dimple the dough by pressing your fingers down into the dough all the way to the bottom of the pan; continue and do this all over different parts of the bread. Sprinkle on fresh rosemary and kosher salt.

Bake the focaccia on the center rack in preheated oven for 20-23 minutes, until golden brown on top. Let cool in pan on wire rack for 10 minutes before slicing and serving.