Bring a pot of water to a boil and add 1 teaspoon of salt.

Add the broccoli and let it cook for 2 minutes. Remove and chop finely.

In the same pot, add the potatoes and cook for 7 minutes until tender. Drain and set aside.

In a saucepan, melt the butter over medium heat.

Add the flour and mix well to form a roux.

Gradually add the milk, stirring constantly to avoid lumps.

Add 1 teaspoon of salt and 1/2 teaspoon of nutmeg.

Continue stirring the sauce until it thickens.

Add half of the grated Parmesan cheese and mix until melted and smooth.

Preheat the oven to 180°C (350°F).

Grease a baking dish with olive oil.

Layer the bottom of the dish with half of the cooked potatoes.

Pour half of the cheese sauce over the potatoes.

Sprinkle with some of the grated Parmesan cheese.

Add a layer of chopped broccoli.

Add the remaining potatoes on top.

Pour the remaining cheese sauce over the top.

Sprinkle with the remaining Parmesan cheese and mozzarella cheese.

Bake in the preheated oven for 35 minutes, or until the top is golden and bubbly.

In a small bowl, combine the Greek yogurt or sour cream, mayonnaise, minced garlic, chopped dill, and parsley.

Mix well.

Once the casserole is baked, remove it from the oven and let it cool slightly before serving.

Serve hot with the prepared topping on the side.