Instructions:

Pasta Preparation: Cook pasta as per package instructions until al dente. Drain and set aside.

Sauce Creation: Melt butter in a large saucepan over medium heat, add flour and stir for 1-2 minutes until a light golden hue appears. Gradually whisk in milk, continuing to stir until sauce thickens. Remove from heat and incorporate sour cream, Dijon mustard, and garlic powder.

Oven Preheating: Set your oven to 375°F (190°C).

Layering the Casserole: In a 9×13-inch baking dish, create the first layer with half of the pasta, sauerkraut, Polish sausage, and half of the Swiss cheese. Gently pour and spread half of the prepared sauce over this layer.