Start by boiling a large pot of water. Cook the tri-colored veggie rotini until it is nice and al dente, usually around 8-10 minutes. Keep an eye on it so it does not become too soft. After cooking, rinse the pasta under cold water in a colander to prevent stickiness.
In a separate pot, blanch the chopped broccoli florets in boiling water for just a couple of minutes until they turn bright green. This quick step will make the broccoli a tad tender while retaining its crunch. Do not overcook; it should remain crisp.
In a large bowl, whisk together the mayonnaise, sugar, and apple cider vinegar until it is smooth and creamy. Ensure that all ingredients are well blended for a consistent creamy texture.
Add the al dente pasta, blanched broccoli, diced red onion, and shredded cheddar cheese to the dressing. Gently toss everything together to coat the pasta and veggies well without squishing the broccoli florets.
Cover the salad and place it in the fridge to chill before serving. The flavors will meld as it cools. Serve it within a couple of hours to maintain the freshness of the mayonnaise.