Prepare the ingredients: Slice the onion and mince the garlic. Separate and rinse the cauliflower florets, cleaning the stem to use as well.
Saute the onion & Garlic: Preheat a pan on medium-low and sauté the onion and garlic in olive oil until golden brown, about four minutes. In a pot, boil the cauliflower in enough water to cover it for fifteen minutes.
Make the bechamel sauce: In a bowl, mix the béchamel sauce with the aromatics, nutmeg, and celery salt. Spread the cauliflower on a baking tray and pour the béchamel sauce mixture over it. Preheat the oven to 150ºC (300ºF).
Bake in the oven: Bake for thirty minutes with a fan, or forty minutes at 180ºC (356ºF) without a fan, until browned. Let it rest for ten minutes before serving to enhance the flavor. Enjoy!