Heat 2 tablespoons of the oil in a large frying pan. Add the celery and onion and fry over a medium heat until the onion has softened and become translucent. Add the garlic and fry for 1 minute, then add the rice and fry for 2 minutes, stirring to coat all the grains in the oil.
Pour the wine into the pan and leave to bubble until all the liquid has evaporated.
Add the stock over a medium heat, a ladleful at a time, stirring continuously. Allow each ladleful of stock to be absorbed before adding the next. Keep adding stock until the rice is cooked but still has a slight bite to it. This should take about 15–20 minutes.
Stir in the butter, then the asparagus and the white and brown crabmeat. Season with salt and pepper.
Mix together the remaining oil and the lemon juice and use to dress the rocket leaves. Serve the risotto in bowls, topped with the dressed rocket leaves.