Bring a pot of salted water to a boil and cook the elbow macaroni according to package directions until al dente, then drain and set aside to cool slightly. While the pasta cooks, prepare your vegetables: peel and seed the cucumber, then cut into small cubes; seed the tomatoes and dice them into similar-sized pieces; finely dice the red onion; and chop the fresh parsley and dill. I like to seed both the cucumbers and tomatoes because it prevents the salad from becoming watery as it sits—this is especially important if you're making it ahead of time.

In a separate bowl, whisk together the mayonnaise, sour cream, cider vinegar, mustard powder, and sugar until smooth and well combined. Add the salt, black pepper, and celery seed, stirring until the spices are evenly distributed throughout the dressing. Taste and adjust seasoning if needed—I often add a touch more vinegar if the salad feels too rich or an extra pinch of salt if the flavors seem muted.

In a large bowl, combine the cooled cooked pasta with the prepared vegetables from Step 1. Pour the dressing from Step 2 over the top and gently fold everything together until all ingredients are evenly coated. Refrigerate for at least 30 minutes before serving to allow the flavors to meld and the salad to chill completely.