Combine the stock and porcini mushrooms in a medium saucepan over medium heat. Bring to the boil. Reduce heat to low and keep at a gentle simmer.
Heat a large saucepan over medium-high heat. Add the sausage and cook, stirring with a wooden spoon to break into lumps, for 2-3 mins or until golden brown. Use a slotted spoon to transfer to a plate. Add the brown mushroom to the pan and cook, stirring, for 2 mins or until tender. Transfer to a separate plate.
Add oil, chopped fennel and onion to large pan. Cook, stirring, for 5 mins or until the fennel and onion soften. Add the rice and cook, stirring, for 2 mins or until the grains appear glassy.
Add wine or extra stock to the rice mixture. Cook, stirring constantly, for 2-3 mins or until the liquid is absorbed. Add ½ cup (125ml) of the stock mixture (with porcini mushroom) and cook, gently stirring constantly, until the liquid is completely absorbed. Repeat with the remaining stock mixture, stirring constantly and allowing liquid to be absorbed before adding more, until rice is tender yet firm to the bite and risotto is creamy (this should take about 20 mins).
Add sausage, brown mushroom and parmesan to the pan. Stir to combine.
Divide the risotto among serving bowls. Top with crème fraîche and the reserved fennel fronds.