Step 1

Fill a large saucepan with water and bring to a boil; season generously with salt. Add the pasta and cook until al dente. Drain well and transfer to a large bowl.

Step 2

In a medium bowl, whisk the buttermilk with the mayonnaise, vinegar, and garlic. Season with salt and pepper. Toss half of the dressing with the warm pasta; let cool for 30 minutes.

Step 3

Meanwhile, fill the saucepan with water and return to a boil; season generously with salt. Set up an ice bath. Add the asparagus and peas to the boiling water and cook until crisp-tender, about 2 minutes. Drain and transfer the vegetables to the ice bath to cool completely; drain well.

Step 4

Stir the asparagus, peas, and remaining dressing into the pasta. Season with salt and pepper, then fold in the arugula and serve.