For the starter dough: Whisk the 5g yeast with the 135ml water until dissolved. In a separate bowl mix the strong white and rye flours until combined. Pour the yeast mixture over the flours and whisk well to form a smooth paste.
Cover with a damp cloth and leave ferment for at least 6 hrs, preferably 18 hrs. You should be able to smell the strong fermentation odours.
For the fougasse dough: Line 4 baking trays with greaseproof paper. Add the 680ml water to the fermented starter dough and mix well to combine.
Place the white bread and dark rye flours into the bowl of a food processor with a dough hook attachment. Add the salt to one side of the bowl and the yeast to the other side. Do not allow them to touch as the salt will start to kill the yeast.
Add the starter dough and water mixture to the bowl and mix on a slow speed for 5 minutes until all the water is absorbed. (This can be done by hand if you don't have a mixer.) Scrape the dough from the sides of the bowl and the dough hook, then continue to mix on a medium speed until the dough is smooth and elastic, 5 to 7 more minutes.
Scrape the dough into a neat ball, then cover the bowl with cling film and allow to prove until doubled in size, about 1 hour. When the dough has finished proving, turn out onto a lightly floured board and cut into 4.
Shaping and preparing the fougasse: Roll each piece of dough into a triangle and place each one onto a baking tray.
Make a cut along the centre of each one, but do not cut through the dough. Make 3 large cuts at either side of the middle cut (think of a leaf), but these cuts must go all the way through dough so you can open them to make holes.
Brush with the oil and scatter over the herbs and olives. Grind some black pepper over each one. Cover with cling film and leave to rise for 30 to 40 minutes.
Preheat the oven to 240 C / Gas 9. Place a baking tray in the bottom of the oven.
Pour 50ml water into the baking tray and put the fougasse in to bake. The steam from the water will help to form a good crust. Bake for 18 to 20 minutes until golden brown and the bottom sounds hollow when tapped. Remove from the oven and leave to cool. ENJOY!