Add 4 cups of pizza flour to a deep bowl. Add 1 teaspoon salt and mix well.
In a separate bowl, add 2 cups of warm water (around 38°C). Add 1.5 teaspoons sugar and 3 teaspoons dry yeast. Mix and set aside for 8 minutes until the yeast activates and becomes frothy.
Make a well in the flour and pour in the yeast water mixture. Mix until a shaggy, sticky dough forms — this is exactly what you want.
Add 3 tablespoons olive oil and fold it into the dough. The dough will be soft, moist and slightly sticky.
Cover the bowl with a moist cloth and proof in a warm place for 1 hour, or until the dough has doubled in size.
Once doubled, fold and mix the dough for about 2 minutes to knock back the air.
Generously oil a baking dish. Transfer the dough and use your fingers to spread it out to the edges.
Proof for a further 20 minutes.
Drizzle 2 tablespoons of olive oil over the top. Scatter a generous handful of fresh rosemary.
Using your fingers, poke deep holes all over the dough — this is the signature focaccia step and keeps it wonderfully soft.
Bake at 180°C in a preheated oven for 15 minutes, until golden on top.
Remove from the oven and immediately add a little butter or extra olive oil over the warm focaccia. Cut and serve hot.