This recipe is best made close to serving.
Combine stock and water in a large saucepan; bring to the boil then reduce heat to simmer gently.
Meanwhile, heat half the butter and half the oil in a separate large saucepan; add mushrooms, cook, stirring, until browned lightly. Add garlic; cook, stirring, until fragrant. Remove from pan, cover to keep warm.
Heat remaining butter and oil in the same pan; cook onion, stirring, until soft. Add rice, stir over a medium heat until the rice is coated in butter mixture. Stir in 1/2 cup (125ml) of the stock mixture, cook, stirring, over a low heat until liquid is absorbed.
Continue adding stock mixture, in 1/2 cup batches, stirring after each addition until liquid is absorbed. Total cooking time should be about 20 minutes or until rice is tender.
Stir in mushroom mixture, parsley, cheese, extra butter and rocket. Season to taste with salt and pepper. Top with extra parmesan cheese flakes, if desired.