Combine the vegetable broth, water, reserved asparagus ends, dark leek greens, and herb stems in a saucepan. Bring to a simmer over medium-high heat, then reduce the heat to low to maintain a gentle simmer for 20 minutes.

Strain the broth through a fine-mesh strainer into a clean bowl, discarding the solids. Return the liquid to the saucepan and keep it warm over low heat.

Melt some of the butter in a large saucepan or Dutch oven over medium-high heat. Add the asparagus spears, peas, and a pinch of salt; cook until the asparagus is tender-crisp and bright green, about 4 to 6 minutes. Transfer the vegetables to a bowl and set aside.

Melt more butter in the same pan over medium-low heat. Add the sliced leeks and a pinch of salt, cooking until they are soft and translucent, about 8 to 10 minutes.

Stir in the garlic and cook until fragrant. Increase the heat to medium, add the rice, and cook, stirring frequently, until the grains are translucent at the edges.

Add the wine and simmer, stirring constantly, until it is completely absorbed by the rice.

Add most of the warm broth and simmer, stirring only occasionally, until the liquid is absorbed and the rice is mostly tender, about 10 to 12 minutes.

Add the remaining broth in small splashes, stirring constantly to release the starches until the rice is creamy and tender but still has a slight bite at the center.

Remove the pan from the heat and stir in the remaining butter, Parmesan, lemon juice, and the cooked asparagus and peas. Cover and let the risotto sit for 2 minutes.

Mix the minced parsley, mint, and lemon zest in a small bowl. Serve the risotto hot, topped with the fresh gremolata.