Rinse the frozen peas to remove any frost; drain and set aside.
Place stock in a saucepan and keep warm over a low heat.
Pour the oil into a large skillet over a medium-high heat. Add the fennel and fry for about 4 minutes, or until softened, but not browned, stirring often. Add the garlic and rice and fry for a minute, stirring constantly, until the grains of rice are coated in the oil.
Pour the wine into the stock, stir and bring to a gentle simmer. Add a ladleful of the hot stock mixture to the rice and simmer, stirring continuously. Wait until the stock is almost fully absorbed before adding the next ladleful. Continue to add the stock, a ladleful at a time, and cook the risotto for 15–20 minutes, or until you are left with about 8 oz stock in the saucepan and the rice is nearly cooked.
Add the peas and lemon juice. Ladle in some of the remaining stock and keep stirring for a couple of minutes. Add the salmon slices, sour cream, tarragon and Parmesan. Stir and continue to cook until the salmon is opaque.
Season to taste with salt and pepper and serve immediately, sprinkled with extra parmesan.