Clean and wash the cauliflower and cut into florets. Bring the water to the boil with a little salt and cook the cauliflower al dente in it. Drain.
Make a roux from butter or margarine, flour, cauliflower water and milk. Season well with salt, pepper and nutmeg. Peel the onion and clove of garlic, cut into fine cubes and sweat in butter or margarine until translucent. Add half of the roux and the spinach leaves. Let it thaw slowly and cook according to the instructions on the package. Season well too.
Let the cauliflower get hot in the rest of the roux.
Arrange the spinach in a wreath on a plate and place the cauliflower in the middle.
Scald tomato and peel off the skin. Cut into small cubes and spread over the cauliflower with the grated cheese.