Mix the flour, yeast and 1/2 tsp salt in a large bowl. Pour in 200ml warm water and the oil, then mix to a rough dough and set aside for 5 mins. It should now feel damp but not overly sticky.
Flour the work surface and your hands, then knead the dough for 5-10 mins. Place in an oiled bowl, cover with oiled cling film, and leave to rise until doubled in size, either for 1 hr in a warm room or overnight in the fridge.
Divide the dough in half, shape into rounds, then leave for 15 mins – if the dough has been in the fridge, it may need to sit for longer. To freeze for up to 1 month, put in an oiled food bag and squeeze out most of the air before sealing. Defrost in the fridge, roll out and use.
Heat oven to 240C/220C fan/gas 9 and slide a baking sheet onto the top shelf. Dust another baking sheet with some of the semolina or flour.
Dust the work surface with a little semolina (try not to use too much as this reduces grip), then roll the dough into a rough oblong about 30cm long. Lift onto the baking sheet and reshape if you need to.
Mix the oil and garlic with seasoning, then toss in the sprouts. Spread 2 tbsp mascarpone over the dough, leaving the edges free, then scatter with the sprouts. Dot with the blue cheese and the remaining mascarpone. Grind over some black pepper, then let the pizza rise for 10 mins at room temperature. Slide the whole thing, baking sheet and all, on top of the hot sheet in the oven and bake for 10-12 mins until golden.