1-First, preheat the oven to 375°F (190°C) and grease a 13 x 9 inch baking dish. This sets the stage for even cooking and prevents sticking, ensuring your bake comes out just right.

2-Next, boil the sliced potatoes in salted water for 5 minutes, then reserve 1 cup of the cooking water. Drain the potatoes and set them aside this step helps them absorb flavors without getting too soft.

3-Now, brown the 1 pound of ground pork sausage in a skillet over medium heat and drain the excess grease. This builds a flavorful base that ties the whole dish together.

4-In a saucepan, melt the 3 tablespoons of margarine or butter, add the 1/4 cup of all-purpose flour, and stir to form a smooth mixture. Gradually whisk in the reserved potato water and 1 cup of milk over medium heat until the sauce thickens, seasoning with salt and black pepper as desired.

5-To assemble, layer the boiled potatoes, optional onions, browned sausage, and optional shredded cheese in the baking dish. Pour the white sauce evenly over the layers, then cover with foil and bake for 45 minutes.

6-For the finishing touch, remove the foil during the last 10 to 15 minutes to let the cheese topping get crispy. Let the casserole rest for 10 minutes before serving this makes about 20 minutes of prep and 45 minutes of cook time, totaling around 1 hour and 5 minutes.