Warm the vegetable broth in a small saucepan over low heat until simmering; keep it gently bubbling throughout cooking.
Trim the tough ends off the asparagus, then cut into 1-inch pieces. Blanch the tips in boiling water for 1 minute, then transfer to an ice bath to stop the cooking and preserve their bright green color. Drain and set aside.
In a large heavy-bottomed pan, heat 2 tablespoons of olive oil over medium heat until it shimmers and you hear a gentle sizzle. Add the finely chopped onion and cook, stirring often, until translucent and fragrant—about 5 minutes.
Add the asparagus pieces (not the tips) to the pan and sauté for 2-3 minutes, just until they start to soften and release their fresh aroma.
Stir in the rinsed Arborio rice, coating each grain in the oil and aromatics. Cook for about 2 minutes until the rice turns slightly translucent around the edges and begins to toast, filling the kitchen with a toasty aroma.
Start adding the warm broth, one ladleful (about ½ cup) at a time, stirring constantly. Wait until most of the liquid is absorbed before adding the next ladleful. Continue this process, stirring gently, for about 20 minutes, until the rice is tender yet still a little firm in the center.
When the rice is nearly done, fold in the blanched asparagus tips and cook for another 2 minutes, stirring gently to distribute evenly.
Remove the pan from heat and stir in the grated Parmesan cheese, butter, and a squeeze of lemon juice. Taste and season with salt and freshly ground pepper as needed.
Let the risotto rest for a minute, then serve immediately, topped with extra Parmesan and a few asparagus tips for a pop of color and freshness.
