Divide the cauliflower into florets, rinse, drain and add them to a microwaveable bowl. Add 2 tablespoons of vegetable broth and cover with plastic wrap.
Microwave the bowl for 5-8 minutes, until cauliflower is cooked through and tender. Discard excess water and allow to cool down for a couple of minutes.
Transfer the cauliflower to a food processor or blender and process until you get a cauliflower rice texture. Add the butter, sour cream and garlic and process until you obtain a texture like mashed potatoes.
Transfer to a bowl and add tomato, celery and chopped scallion, mix thoroughly. Season with salt and pepper to taste.
Transfer to a baking dish and top the loaded cauliflower with cheese and scallion. Place under the broiler for a few minutes to melt the cheese, serve immediately.
