In a large bowl, combine flour, yeast, sugar and a generous pinch of salt.
Make a well in the center, and mix in half of the olive oil and the water.
Using a fork and then your hands, work the dough until it comes together. It should be soft and slightly sticky. Pick up the dough and throw it back into the bowl a couple of times.
Pour a generous amount of olive oil over the top of the dough, making sure to coat all of the dough and the bowl in the oil. Cover with plastic wrap and let rise in a warm place until doubled in size (about 1-2 hours).
Punch down the dough and put it into a greased 9x13in sheet pan. Stretch out the dough until it reaches the corners, and press into it with your fingers multiple times. Cover with plastic wrap and let rise for 30 minutes.
Preheat the oven to 425°F/220°C. Sprinkle some salt – and, if using, herbs and other toppings – over the top of the dough and bake until golden, about 20 minutes.
While the focaccia is still hot, pour the remaining half of the olive oil over the top and sprinkle with more salt. Serve warm.