To active yeast, combine sugar, lukewarm water in a small bowl and add yeast. Let it sit for 10 minutes or until yeast is foamy.
Place flour and salt in a large bowl, add the yeast mixture and 2 tablespoons of oil. Gently stir with your hand until it forms a dough. On a floured surface knead for 8-10 minutes.
Return dough to bowl, cover and let it rest for 60-90 minutes or until it's double in size.
In the meantime, wash and finely chop the rosemary and mix with 3 tablespoons of olive oil. Let it sit until dough is ready.
Line two large baking sheets with baking paper.
Get the dough out of the bowl and divide in two parts.
On a floured surface, roll it out into a large rectangle until the dough is 1/2-inch thick.
Cover the dough with a towel and let it sit for another 30 minutes.
In the meantime, thinly cut the blackberries crosswise into 3-4 slices.
Preheat oven to 400°F.
Remove towel and use your fingers to poke deep dents. Press the blackberry slices into those dents.
Drizzle the loaves with the rosemary oil and spread it with a brush or your fingers. Sprinkle with flaky salt.
Bake for 20 minutes but turn up heat very high the last 3-5 minutes. Be careful not to burn it. Slice and serve warm.