Preheat oven to 400 + spray an 8x10 inch oven safe serving dish.
Fill large pot with about 2 inches of salted water. Set up your steamer basket + add in the cauliflower florets. Place the lid on + steam for about 5-7 minutes or until the cauliflower is tender but still has a crunch. Check with a fork! Then drain all water + set aside.
Place a medium skillet over medium-high heat + melt your butter/ghee.
Add in onions + sauté until translucent, about 4 minutes. Add in the garlic + flour, stirring constantly cook for 1 minute.
Gradually pour in your milk + pepper to taste. Cook stirring constantly to dissolve all lumps, until mixture starts to thicken, about 3 minutes.
Stir in 3/4 cup cheddar + all Parmesan cheese, continue stirring until completely melted.
Ladle about 1/3 of this cheese sauce into the baking dish.
Layer in your steamed (completely drained of moisture by now) cauliflower.
Spoon over the remaining cheese sauce + spread as evenly as you can.
Sprinkle with the remaining 1/4 cup cheddar cheese + bake, uncovered for about 14 minutes in your preheated oven.
For extra golden topping, broil during the final 2-3 minutes of baking time.
Allow to cool for several minutes, garnish with fresh parsley + serve warm.