1. Bring a large pot of salted water to a boil. Cook macaroni pasta until al dente. During the last few minutes of cooking, add the broccoli florets to the boiling water. Drain everything together in a colander.
2. Meanwhile, in a large saucepan, melt the butter. Add the onion, garlic, chili flakes and cook for 5-8 minutes or until soften. Add the flour and stir to cook. Slowly whisk in the milk.
3. Bring to a boil and cook until thickened, about 3-5 minutes. Whisk in the sweet chili sauce and shredded cheese until melted.
4. Toss together the pasta, broccoli, and sauce then serve hot.