2) In a large saute pan over a medium-low heat add 2 tbsp of olive oil. Add the onions and slowly caramelize until brown and creamy, about 20 minutes. Set aside to cool.
3) Preheat the oven to 240C/Gas 9. Preheat the griddle to a medium-high heat and wipe down with oiled paper towels to create a non-stick surface.
4) On a plain floured surface, roll out each of the pizza dough into an elongated shape, about 30cm by 20cm and about 1cm thick. Brush with olive oil and griddle on both sides until warmed through and griddle marked, about 4 minutes per side. Transfer to a baking sheet.
5) In a medium bowl, mix together the mascarpone and blue cheese. Smear the cheese mixture over each of the griddled pizza crusts. Place in the oven for 2 to 3 minutes until the cheese melts. Remove from the oven and transfer to a cutting board or platter.
6) Top with caramelized onions, toasted walnuts and fresh grapes. Season with salt and a few turns of freshly ground black pepper, drizzle with some more extra-virgin olive oil and top with fresh parsley.