Boil the Pasta and Broccoli: In a large pot, bring salted water to a rolling boil. Add penne pasta and cook according to package instructions. When there are about 2 minutes left, add fresh broccoli florets into the pot. Once cooked, drain the pasta and broccoli, then set them aside in a colander to allow steam to escape.

Sauté Kielbasa: Heat a large skillet over medium heat and add unsalted butter. Once melted and bubbly, add sliced kielbasa and cook for about 5 minutes, stirring occasionally, until lightly browned and fragrant.

Add Aromatics: Stir in diced yellow onion and minced garlic with the browned kielbasa. Cook for an additional 2-3 minutes, stirring frequently, until the onion is soft and translucent.

Create the Creamy Sauce: In a small bowl, whisk together cornstarch and whole milk until smooth. Pour this mixture into the skillet. Bring to a gentle simmer, stirring continuously until the sauce thickens, about 3-5 minutes.

Incorporate Cheese: Reduce heat to low and gradually stir in shredded cheddar cheese, mixing until melted and smooth.

Combine Pasta and Broccoli: Add drained penne pasta and broccoli to the skillet, gently tossing them in the cheesy sauce. Season with salt and pepper.

Serve and Garnish: Once combined and heated through, remove from heat. Garnish with fresh parsley and serve immediately.