Boil a large pot of salted water over high heat. Add penne pasta and cook according to package instructions until al dente, about 10 minutes. Stir in broccoli florets during the last two minutes of cooking.

In a large skillet over medium heat, melt butter until bubbly. Add sliced kielbasa and cook for 5 minutes until golden brown.

Add diced onion and minced garlic to the skillet. Sauté for another 2 to 3 minutes until the onion is soft.

In a small bowl, whisk together cornstarch and whole milk until smooth. Pour into the skillet, stirring as it heats. Simmer for 3 to 5 minutes until thickened.

Reduce heat to low and gradually add shredded cheddar cheese. Stir until the cheese melts completely.

Add cooked penne and broccoli to the skillet, tossing until well-coated with the sauce. Adjust seasoning with salt and pepper.

Serve hot, garnished with fresh parsley.