Put the bread mix in a large bowl with 310ml warm water, 1 tablespoon of the oil and half the chopped rosemary. Mix to a dough, then knead on a floured surface for 5-10 minutes, until smooth. Place in another lightly oiled bowl and cover with lightly oiled cling film. Leave in a warm place for 1 hour, until it has risen to double its size.
Meanwhile, mix the garlic and crème fraîche together in a small bowl. Set aside. Put the potato and broccoli in a microwave-safe bowl with 1 tablespoon water, cover and cook on high for 2-3 minutes. Drain, then add the onion and most of the remaining rosemary. Season with black pepper.
Preheat the oven to 220°C, fan 200°C, gas 7 and place 2 baking sheets in the oven to heat up. Knead the dough for a minute, then divide into 2. On a floured surface, roll out each piece into a large rectangle.
Place each dough base on a hot baking sheet, then spoon over the garlic crème fraîche. Scatter over the potato, broccoli and onion mix, then top with the mozzarella and remaining rosemary. Drizzle over the remaining oil and bake for 15-20 minutes, until crisp and golden.