Trim woody ends off asparagus. Cut into 1-2 inch pieces.
In a saucepan, heat broth and 1 cup water over med-low heat.
In another large pan, saute chopped onion and minced garlic over med-high heat for about 7 minutes.
Add the rice and cook, stirring constantly for 2-3 minutes.
Mix water and vinegar in a cup.
Add the diluted vinegar and cook until liquid has absorbed.
Start adding the warmed broth, 1/2 cup at a time. Stir occasionally and wait for the liquid to be absorbed before adding the next 1/2 cup.
Meanwhile, saute mushrooms (if using) and asparagus until tender, about 4 minutes.
When all the broth has been absorbed by the risotto, remove pan from heat.
Add asparagus, salt/pepper, and parmesan and serve immediately.