Slice the radishes and zucchini into very thin rounds, approximately 1/8″ (a mandolin slicer makes this job quick and easy)
Cut the cauliflower into florets. You can also use the cauliflower stems; cut those into small pieces
Bring the water to a simmer over medium-high heat and add the cauliflower
Simmer the cauliflower until slightly overcooked, about 15 minutes
Meanwhile, preheat the oven to 375F
Pour the water and the cauliflower into a blender
Add the ghee and blend on high until you have a completely smooth puree (20 seconds to a minute, depending on your blender)
Beat the egg slightly in a bowl and then temper the egg by adding a spoonful of the hot cauliflower puree to the egg while stirring vigorously. (Add another spoonful the same way and then a third spoonful.)
Add the tempered egg to the cauliflower puree and blend to combine
Add salt and pepper to taste
Lay the radish and zucchini slices to the bottom of a 9″ x 9″ casserole pan or baking pan and pour the cauliflower puree over the top
Stir to make sure the veggie slices are well coated in the sauce and then smooth out to make sure the veggie slices are all lying flat
Bake for 30 minutes, until bubbling and the veggies are soft with just a little bit of give when pierced with a knife
To brown the top layer, broil for 3 to 5 minutes at the end