Cook the ditalini pasta in salted water until al dente, according to package instructions. Before draining, reserve about 1 cup of pasta water. Drain the pasta and return it to the pot.
Add the mascarpone, basil pesto, lemon juice, and a splash of the reserved pasta water to the warm pasta. Stir until the mascarpone melts and everything comes together in a creamy, glossy sauce. Add more pasta water as needed to reach your desired consistency.
While the pasta cooks, prep the spring veggies. Heat the olive oil in a large pan over medium heat. Add the leeks and a generous pinch of Kosher salt. Cook for about 8 minutes, stirring occasionally, until softened.
Add the minced garlic and red pepper flakes. Stir constantly and cook for 1 minute. Pour in the white wine and scrape the bottom of the pan with a wooden spoon to release any browned bits. Let it simmer for 2–3 minutes, until most of the liquid has evaporated.
Add the sliced asparagus and peas. Toss to combine and cook for about 2 minutes, just until the veggies are bright and crisp-tender. Season to taste with Kosher salt and black pepper.
Stir the cooked veggies into the prepared pasta. Divide the pasta among bowls and top with lemon zest, extra lemon juice, and Parmesan cheese, if desired.
