Heat ½ cup chicken stock and Stilton in a small saucepan over medium heat, stirring, until cheese is just melted. Place remaining stock in a saucepan and bring to a simmer.
Heat half the butter in a heavy-based saucepan, add onion and cook over medium heat for 5-7 minutes or until soft, then add rice and stir for another 5 minutes. Gradually add half the simmering stock and stir over low heat until liquid is absorbed, then add remaining stock, ½ cup at a time, stirring continuously, allowing each addition to be absorbed before adding the next.
When rice is al dente, stir in remaining butter, Stilton mixture and ham, then season to taste with sea salt and freshly ground black pepper and serve immediately, with a green salad passed separately.