Add butter to a 9x13 oven safe dish and spread it around the bottom of the dish with your fingers. Drizzle olive oil around the dish.
Add all purpose flour, instant yeast, sugar and salt to a mixing bowl. Mix together.
Add warm water and olive oil and mix it into a dough.
Pour the dough out into your prepared 9x13 dish. Don't worry to spread it out in any way, however it lands in the dish, just leave it be.
Cover the dish and leave to rise for 1 hour.
After 1 hour you'll see that the dough has risen and spread to the edges of the dish.
Preheat the oven to 425°F (220°C).
Rub your fingers with olive oil and then use your fingers to poke holes in the dough, all over the surface of the dough.
Sprinkle fresh rosemary on top along with a sprinkle of sea salt. Drizzle olive oil over the surface of the dough.
Bake for 20 minutes until golden and crispy on top.
Slice and serve the focaccia directly from the dish or transfer it to a wooden board, cut into squares and serve warm.