Sauté the onion and garlic in the oil. Add the rice, sauté and stir until translucent. Stirring frequently, add the bouillon a little at a time so that the rice is always just covered with liquid, simmer for approx. 15 mins. Add the asparagus after 5 mins. and continue to simmer for approx. 10 mins. Once the rice is just al dente, stir in the mascarpone and parmesan, add the champagne and truffle oil, season. Cover and leave to absorb for approx. 1 min. If desired, drizzle/grate a little truffle on top before serving.