Cook the noodles according to the package directions and drain once done. I like to cook my noodles ahead of time and then let them cool before mixing the salad together. You could even make them a day ahead and refrigerate if needed.
In a small mixing bowl, whisk together the mayo, sour cream, vinegar, sugar, mustard, and water or milk. In a large bowl, add the cooked noodles, broccoli, bell pepper, onion, and hard boiled egg. Drizzle on the dressing and stir until everything gets well coated. Taste and add salt and pepper.
There are few things you might consider substituting if you want to make this a little healthier. First, you can swap the noodles for whole wheat or a gluten-free option. The mayo can be substituted for a light version or an alternative. And the sour cream could be subbed for greek yogurt (full fat or a lower fat version).