In a large bowl, dissolve yeast and sugar in water and let stand for 10 minutes or until foam develops on the top. Add oil (1/4 cup), flour and salt and mix to combine the ingredients.

On a lightly floured surface knead into smooth dough, about 15-17 minutes. Drop a tablespoon of oil in a large bowl and roll the dough in the bowl to evenly coat with oil. Cover the bowl and set aside in a warm place for 1 1/2 hour or until the volume doubles.
Tip the dough on to an oiled quarter sheet pan and stretch it to the size of the pan. Cover with a kitchen towel and set aside in a warm place for an hour or until the volume doubles.

Preheat the oven to 220°C/425°F. Heat a tablespoon of oil in a frying pan and cook onions to golden brown. Add the garlic and rosemary and season with crushed black pepper and salt. Spread the onions on the dough and create dimples by pressing your fingers to the bottom of the dough, at a gap of an inch. Bake for 20-25 minutes or until brown.

Cut Focaccia into squares and serve immediately. Store wrapped in a foil sheet for up to a day.

Variations: Knead 1/2 cup grated parmesan cheese into the dough. In place of onion-garlic topping, sprinkle 1 tbsp chopped rosemary and coarse salt on top.