To a medium bowl, add the buttermilk, mayonnaise, parsley, green onions, salt, mustard, pepper and garlic powder. Whisk until smooth. Give it a taste and adjust the salt to taste.
To Make the Seven-Layered Pasta Salad:
Bring a pot of salted water to a boil. Pour in the pasta and cook until al dente, about 8 minutes. Drain and rinse with cold water. I usually wouldn’t rinse pasta but we’re making pasta salad and we don’t want the pasta to overcook. Drizzle the pasta with about 2 teaspoons of olive oil and give it a good mix. You can do this all in the colander; we’re doing this so the pasta doesn’t stick.
To a glass bowl—we gotta see the layers!—add the dressing. Top it with the pasta. Don’t be shy to arrange it into one even layer. Repeat with the cherry tomatoes, radishes, snap peas and arugula. Top with boiled egg quarters. This is a great make-ahead salad.
Right when you’re ready to serve the salad, toss it all together and divide amongst bowls.