Creamy Seafood Risotto

Name: Creamy Seafood Risotto
Ingredients: 3 c. bottled clam juice; 2½ c. water; 2 tbsp. extra-virgin olive oil; 1 small onion; Salt and freshly ground pepper; 1½ c. arborio rice; pinch saffron threads; ½ c. dry white wine; 1 tbsp. unsalted butter; 1 shallot; ½ lb. cooked shrimp; ½ lb. lump crabmeat; 2 tbsp. flat-leaf parsley; ½ c. mascarpone cheese