Clean, wash and roughly grate the cauliflower. Grate cheese finely. Mix cauliflower, egg and cheese. Season with salt. Line two trays with baking paper. Halve the cauliflower mixture, press each half on a tray to form a flat tarte flambée base (approx. 28 cm Ø). Pre-bake one after the other in a preheated oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer) for about 10 minutes.
Meanwhile peel and finely chop the garlic. Mix sour cream and garlic, season with salt and pepper. Finely dice the ham. Clean and wash spring onions and cut into rings. Wash thyme, shake dry and remove the leaves. Wash and halve the tomatoes.
Spread the sour cream on the cauliflower bases and smooth it down. Cover with ham, spring onions and tomatoes and sprinkle with thyme. Bake one after the other in a preheated oven at the same temperature for about 12 minutes.
Grate the cauliflower with the stalk on the coarse side of a kitchen grater. It is even faster with a universal chopper: chop the cabbage into small portions.