Bring the vegetable broth to a gentle simmer in a small saucepan, keeping it warm throughout the cooking process.
Trim the woody ends off the asparagus and slice the tender parts on a bias into 1-inch pieces. Set aside.
Heat olive oil in your medium pan over medium heat; add finely chopped onion and cook until translucent and fragrant, about 3-4 minutes, stirring often.
Add the Arborio rice to the pan and stir constantly for about 2 minutes, toasting until edges look translucent and smell nutty.
If using, pour in a splash of white wine and stir until mostly absorbed, about 1 minute, adding flavor and brightness.
Start ladling in the warm broth, about ½ cup at a time, stirring gently and continuously, allowing each addition to be absorbed before adding more. Maintain a gentle simmer.
After about 10 minutes, stir in the sliced asparagus. Continue adding broth gradually and stirring, cooking until the rice is tender but still with a slight bite, about 15-18 minutes total.
Check the consistency—risotto should be creamy and the rice tender but not mushy. If needed, add more broth or cook a minute longer.
Remove the pan from heat and stir in the butter and grated Parmesan until melted and silky. Add lemon zest and season with salt and pepper to taste.
Let the risotto rest for a minute, then serve immediately, garnished with extra Parmesan if desired and a drizzle of olive oil for shine.