Preheat the oven to 180°C (350°F).
Prepare the vegetables:
Broccoli: Wash the broccoli, cut into florets, then finely chop. Bring a pan of water to the boil, add 1 teaspoon of salt and blanch the broccoli for 2 minutes. Drain and set aside.
Potatoes: Peel and cut potatoes into slices or cubes. In the same pot, bring water to a boil, add another teaspoon of salt and cook potatoes for about 7 minutes or until tender. Drain and set aside.
Make the cheese sauce:
In a saucepan, melt the butter over medium heat. Add the flour and stir for about 1 minute to create a roux.
Gradually add the milk, whisking constantly to avoid lumps. Add 1 teaspoon of salt and the nutmeg. Continue cooking, stirring constantly, until the sauce thickens.
Reduce the heat and add half of the Parmesan cheese. Stir until the cheese is melted and the sauce is smooth.
Assemble the baking dish:
Grease a baking dish with olive oil.
Arrange half of the potato slices in the bottom of the dish. Pour some of the cheese sauce over the potatoes. Add a layer of broccoli and half of the mozzarella cheese.
Repeat the layers, finishing with a layer of cheese on top.
Bake: Place in preheated oven and bake for 35 minutes, or until top is golden brown and bubbly.
Make the herb topping:
In a small bowl, mix together the Greek yogurt (or sour cream), mayonnaise, minced garlic, dill and parsley.
To serve: Once cooked, let cool slightly. Serve with a spoonful of herb garnish.
