In a medium sized bowl, add the yeast, sugar, and warm water. Let it sit for 5 minutes, until bubbly.
In a stand mixer bowl fitted with a dough hook attachment, add in the flour and salt. Turn on the mixer on low and add in the yeast mixture. Pour in the oil and knead for 5 minutes on low-medium speed, or until the dough is smooth, shiny, and elastic.
Transfer the dough to a lightly greased bowl and cover with plastic wrap or damp cloth. Let it double in size for about 40 minutes in a warm area of your house.
Preheat oven to 425°F/218°C.
Place a piece of parchment paper in a 9" by 13" baking pan.
Once the dough has doubled in size, use your hands to press the air out of the dough and transfer it to the prepared baking pan.
Use your fingers to make dimples in the dough. (Tip: make a fist with your hand and make a rolling motion to make the dimples with the joints of your fingers more quickly).
Drizzle olive oil, sprinkle on the chopped rosemary and fleur de sel on top.
Bake at 425°F/218°C for 20 minutes, or until lightly golden brown.
Remove from oven. Let cool completely before slicing.
Serve with olive oil or use in sandwiches. Can be frozen for up to 1 month, wrapped and sealed in a freezer bag.