Spring Peas and Greens with Cacio e Pepe Dressing

Name: Spring Peas and Greens with Cacio e Pepe Dressing
Ingredients: 1 large egg yolk; 3 tablespoons buttermilk; 1 small garlic clove, finely grated; 1/2 cup extra-virgin olive oil; 3 tablespoons finely grated Parmigiano-Reggiano cheese plus more for garnish; 3/4 teaspoon coarsely cracked black peppercorns; Kosher salt; 2 pounds fava beans, shelled (2 cups); 2 cups fresh or frozen peas, thawed; 4 cups spring greens, such as pea tendrils or baby arugula (2 ounces); 1 Hass avocado, peeled and cut into thin wedges