Put the yeast in a jug with the honey. Add 300ml warm water and stir. Put the flour in a large bowl; stir in 1 tsp sea salt flakes. Make a well in the centre and pour in the yeast water and 2 tbsp oil. Slowly mix the liquid into the flour until it is all combined.
If it feels on the dry side, add a splash more warm water. Turn the dough out onto a lightly floured surface and knead for 10 minutes, until smooth and springy.
Put the dough in a clean, oiled bowl, cover and leave in a warm place for 1-2 hours, until the dough has doubled in size.
Turn out the proved dough into a 35cm x 25cm oiled, rimmed baking tray; knock out the air. Shape into a rectangle just smaller than the tray, loosely cover and leave in a warm place to prove for about 30-45 minutes, until roughly doubled in size.
When the dough is almost ready, preheat the oven to 180˚C, gas mark 4. Put the grapes in a mixing bowl with the rosemary, sugar, pepper, 1 tbsp oil and remaining ½ tsp salt.
Mix together well, then evenly press into the dough. Bake for 35-40 minutes, until golden and cooked through. Drizzle with the remaining 2 tbsp oil and leave for a few minutes before serving.