Combine warm water, yeast and sugar in a small bowl. Set aside until the yeast in bubbly about 15 minutes.
In the bowl of a mixer fitted with a dough hook, combine the flour, salt, 1/2 cup olive oil and the yeast mixture. Mix on low speed until the dough starts to come together. Increase mixer speed to medium and continue to knead 5 minutes or until the dough becomes smooth and soft.
Lightly coat the inside of a large bowl with olive oil and place the dough, turning it to coat the dough. Cover and put it in a warm, draft free part of your kitchen to rest until it has doubled in size, about 1 to 1 1/2 hours depending on how warm your kitchen may be. Don't rush this step as it makes a big difference on the final baked product.
Coat a rimmed baking sheet with the remaining 1/2 cup olive oil. Gently tip the dough into the pan and, using your fingertips, press the dough to fit the pan. Turn the dough over (to coat both sides) and continue to stretch the dough to fit the pan. The dough should be heavily dimpled and, possibly have holes through it. No worries as when it rises these will somewhat fill in. Cover and set aside in a warm place until it has doubled in size, about an hour. The dough will look light an airy when the rise is complete.
When the dough is almost done rising, preheat the oven to 425 degrees F.
Drizzle the top of the focaccia dough with a bit more olive oil and sprinkle with flakey sea salt. Bake until the top is golden brown, 25 to 30 minutes. Remove from oven and (if you can resist) let cool before cutting.