Cook macaroni according to package directions in salted water. Drain and set aside.
While pasta cooks, prepare frozen broccoli according to package directions (microwave or stovetop).
In the same pot you cooked the pasta in, melt butter over medium heat. Whisk in flour and cook for 1 minute, stirring constantly.
Gradually whisk in milk and continue whisking until the mixture thickens, about 3-5 minutes.
Remove from heat and stir in shredded cheese until completely melted. Add salt, pepper, and garlic powder.
Add cooked macaroni back to the pot and stir until everything is coated in cheese sauce.
Serve hot with broccoli on the side (or stir some right into the mac and cheese if your kids will go for it!).