Place artichokes in a medium-size bowl, sprinkle with lemon juice, and set aside. Bring a medium saucepan of water to a boil. Add the asparagus spears and blanch roughly two minutes, or until they’re tender but still have a bit of crunch. Remove them from the pan and run under cold water to stop them from cooking further. Place asparagus in a bowl and add to the bowl with the artichoke hearts. (Save the cooking liquid to add to risotto.)
Heat 1-1/2 tablespoons of the olive oil in a large pot or Dutch oven. Add mushrooms and cook on medium heat until they brown lightly and soften. Add the mushrooms to the bowl with asparagus and artichokes.
Add the remaining 1-1/2 tablespoons of oil. When heated, add the onions and cook for 4 minutes, or until they begin to soften. Add the garlic and cook another 3 minutes.
Add the rice, stirring constantly, for about 2 minutes. Lower the heat to medium-low. Scrape the seeds from the vanilla bean (if using) into the white wine, lemon juice, and lemon zest, and cook, stirring gently but consistently, until the wine is absorbed. (Save the bean itself for your sugar jar.)
Add a cup of broth to the pan and cook, stirring as needed, until the liquid is absorbed. Continue adding broth in 1/2-cup amounts, stirring until the broth is absorbed. (You may not need all five cups of broth to make the rice creamy and soft.) When the rice is tender but still has a slight chew, stir in the vanilla extract (if using) and thyme, along with salt and pepper to taste. Stir the artichoke hearts, asparagus and mushrooms into the rice and heat through. Add the Parmesan and blend thoroughly into the rice.
Spoon Risotto into a serving bowl. Garnish with chopped parsley or chopped chives if desired, and serve additional cheese in a bowl.