Add the yeast and sugar to 350ml (12fl oz) warm water. Stir and set aside.
In a large bowl, combine the flour, fennel seeds, chopped rosemary and 1tsp salt. Add the yeasty liquid, mixing with a wooden spoon until it forms a dough (if it sticks to the bowl, add a little more flour). Using your hands, knead for 10 minutes until smooth.
Pour 1tbsp of the oil into a bowl. Roll the dough in the oil and shape into a ball. Cover with clingfilm and leave in a warm, draught-free place for 1–2 hours until the dough has doubled in size.
Remove the clingfilm and knead half the grapes through the dough, knocking out some of the air as you go.
Scatter a large baking tray with the semolina, polenta or flour (this helps it glide off the tray more easily), then, using your hands or a rolling pin, stretch out the dough, until roughly the size of the tray. Cover with a tea towel and leave to rise for a further 30 minutes.
Meanwhile, preheat the oven to gas 6, 200℃, fan 180℃ and put a lined baking sheet in to heat up.
With your thumb or finger, add indentations into the surface of the dough, press the remaining grapes and some rosemary sprigs, then drizzle with the remaining oil and scatter with sea salt and the extra fennel seeds. Slide the dough on to the preheated tray and bake for 25-30 minutes until golden. Serve warm.
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