This recipe makes the most of asparagus and peas when they are sweet and tender in the springtime. You don't need much more than s few spoonfuls of crème fraîche and generous squeeze of fresh lemon juice to make a nourishing pasta that you will want to come back to every spring.
While the pasta cooks, heat the olive oil in a large pan over medium. Add the onions and sauté until tender, 3 minutes or so. Add the asparagus, snap peas, English peas, salt, and pepper and sauté until crisp/tender, 3 to 4 minutes (they should still have a little snap to them, but no starchiness).
Add pasta to the pan with the vegetables set over low heat. Add the lemon zest and juice, crème fraîche, mint, Parmesan, and a few tablespoons of the pasta cooking water. Taste and add more salt, more freshly ground black pepper, and more pasta cooking water as needed.
Serve immediately with more Parmesan to add at the table.
Crème fraîche is a French-style cultured cream that is rich, thick, and slightly tangy. It's sold in the dairy or cheese section of the market and is also easy to make (though it takes several days). If you can't get crème fraîche, substitute sour cream or full-fat Greek yogurt and cut the amount of lemon juice in half.