Bring a large pot of salted water to a boil and cook the pasta for 6-8 minutes until al dente. Drain and set aside.

Heat olive oil in a large pot over medium/high heat. Add diced onion and sauté for 2 minutes. Add minced garlic and broccoli; season with ¾ teaspoon salt. Cook for 2-3 minutes until broccoli is green and slightly tender. Remove vegetables from the pot.

In the same pot, prepare a roux by melting butter over medium/high heat. Add flour and whisk until combined. Cook for 1 minute.

Gradually add milk to the roux, whisking constantly. Cook for 4-6 minutes until the mixture thickens.

Remove sauce from heat. Add shredded cheddar cheese and whisk until melted. Stir in Parmesan cheese and garlic powder.

Mix cooked pasta and vegetables into the cheese sauce, stirring to coat. If mixture is sticky, rinse pasta under warm water before adding. Serve immediately.