Bring a large pot of salted water to a boil over high heat and add penne pasta. Cook according to the package instructions, usually about 8-10 minutes. In the last 2 minutes of cooking, add the fresh broccoli florets to the pot. Once cooked, drain the pasta and broccoli in a colander and set aside.

In a large skillet, melt 2 tablespoons of unsalted butter over medium heat. Once the butter is melted, add the sliced kielbasa sausage. Sauté for about 5 minutes, stirring occasionally, until the kielbasa is nicely browned.

Stir in the finely diced yellow onion and minced garlic to the skillet with kielbasa. Cook for 2-3 minutes until the onion becomes soft and translucent.

Whisk together 1 1/2 cups of whole milk and cornstarch until smooth. Pour this mixture into the skillet, stirring constantly, and bring to a gentle simmer to thicken.

Reduce the heat to low and gradually add 1 1/2 cups of shredded cheddar cheese, stirring continuously until fully melted, creating a rich creamy texture.

Add the drained pasta and cooked broccoli to the skillet, tossing gently to coat in the creamy cheese sauce. Season with salt and pepper to taste.

Remove the skillet from heat, serve generous portions onto plates, and garnish as desired. Serve hot.