1. Preheat the oven to 350°F (175°C). Preheating ensures your casserole bakes evenly and allows all those cozy flavors to mingle perfectly. (Lightly grease a 9 x 13-inch baking dish with non-stick cooking spray. This simple step prevents sticking and makes cleanup a breeze later on.)

Prepare the potatoes:

1. Peel and cube the russet potatoes evenly. In a medium saucepan, bring water to a boil and cook the potatoes for approximately 7 minutes or until just tender. Drain the potatoes and transfer them to a greased 9 x 13-inch the prepared baking dish.

Cook the kielbasa:

1. Heat olive oil in a skillet over medium heat. Add the kielbasa slices and sauté until lightly browned, about 5 minutes. Remove from heat and distribute the kielbasa over the potatoes in the baking dish.

Create the roux:

1. In the same skillet, melt the butter over medium-low heat. Gradually whisk in the flour until the mixture forms a smooth paste. Cook for 1-2 minutes, stirring constantly, to eliminate the raw flour taste.

Prepare the sauce:

1. Add minced garlic to the roux and stir briefly until fragrant. Slowly pour in the milk and heavy cream while whisking continuously. Add cumin, garlic powder, salt, and black pepper. This blend of seasonings perfectly complements the smoky richness of the kielbasa, adding a gentle warmth that brings all the flavors together. Stir to combine, allowing the spices to bloom and infuse the sauce as it thickens. Stir in the cheddar cheese soup and cook until the sauce thickens, approximately 3-4 minutes.

Incorporate the cheese:

1. Remove the skillet from heat and fold in the shredded cheddar cheese. Stir until the cheese has melted completely and the sauce is smooth.

Assemble the casserole:

1. Pour the cheese sauce evenly over the potatoes and kielbasa in the baking dish, ensuring all ingredients are well-coated.

Bake:

1. Place the dish in the preheated oven and bake for 30 minutes, or until the top is golden brown and the sauce is bubbly. Allow the casserole to rest for 5 minutes before serving.