Place the potatoes into a large pot and cover them with cold water (cold water will ensure an even cook-through). You don’t need to either peel or cut the potatoes before boiling – this way you ensure minimal flavor loss! Boil your potatoes for about 20-25 minutes or until a fork comes through easily. When the potatoes are done, place them under cold water to cool down. After the potatoes are at room temperature you can peel them by simply pulling the skins off with your hand or with a knife. Slice the potatoes into round pieces and set them aside.
While the potatoes are boiling you can boil the eggs. Place the eggs into a medium size pot and cover with cold water. Bring to a boil and cook for 10 minutes. Turn the heat off and place the eggs under cold water to cool down. Once cooled, peel the eggs and slice them into small pieces.
While the eggs and the potatoes are cooking you can start working on your bechamel sauce. Place the butter into a medium size saucepan and set on the stove at low-medium heat. Make sure the butter down burn as it melts. Once the butter has melted, add the flour and stir with a rubber spatula or a whisk to prevent lumps from forming.
Once the mixture has been incorporated, pour the milk in and continue stirring. You can bring the heat up a bit at this point to speed up the process, just make sure your milk doesn’t burn on the bottom. Once you see that the sauce is starting to thicken add chopped or grated garlic, ground nutmeg, salt, and pepper. Continue stirring until the sauce is at the desired thickness, then turn the stove off and set the sauce aside.
Chop the onion and the sausage and set them aside. UPDATE: for more flavor, caramelize onions before adding to the casserole! For this you will need to use 4 onions instead of 1.
Time to assemble the casserole! Spread a little bit of bechamel sauce on the bottom of the baking dish. Then, place the first layer of potatoes, eggs, sausage, and cover with a layer of bechamel sauce (use a spoon or a spatula to carefully spread the sauce across the dish). Repeat all the layers once again, then cover with shredded cheese on top. If you have any leftover ingredients, you can place them on the top first, and then add the cheese.
UPDATE: for more flavor, add cheese on top of each layer. You can use a cheaper kind than cheddar, it will still taste delicious!
Place the casserole into a preheated oven at 350F (170C) and bake for about 20 minutes. During baking the sausage lets its juices out, the bechamel sauce penetrates into the rest of the ingredients, and the cheese melts creating a flavorful top for your dish. Once the casserole is baked through, serve it as soon as you’d like to!