Preheat a wood fire oven to 600°F-700°F, or a conventional oven to it's highest setting.
Pour the water into a bowl and whisk the flour in a little at a time. Continue whisking until the flour is fully incorporated and there are no lumps. If you have an immersion blender, it is a tremendous help.
Allow the mixture to sit for 4-6 hours.
Preheat the pan in the oven.
After the mixture has rested, skim the top and remove any foam that may have formed.
Then, add the salt and the chopped rosemary and stir until well combined.
Remove the pan from the oven and pour in the olive oil, coating the bottom of the pan evenly.
Pour the farinata batter in slowly so it doesn't displace the olive oil. To make it easier, you can pour the batter onto a spoon and let it slide off the spoon and into the pan. No matter how you choose to do it, the batter should float on top of the oil.
Put the pan in the oven. Use the guide below to determine your cooking time:The oven should be as hot as possible. At 500°F, it should take about 15 to 20 minutes and then broil for a few minutes. Keep an eye on it to make sure it doesn't burn. You can brush it with olive oil to create a crunchier crust if you like. At 600°F - 700°F it should take about 5 to 7 minutes. Remove from the oven, add a few cracks of black pepper and a sprinkling of sea salt, slice and serve!