Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Wash sweet potatoes thoroughly, dry them and place them on a baking tray lined with baking paper. Bake in a hot oven for 25-30 minutes.
In the meantime peel and finely dice the shallot. Drain the beetroot and dice finely. (Important: Wear disposable gloves, colour the beetroots!) Drain the corn in a sieve. Wash thyme, shake dry, remove leaves and chop finely.
Pluck the mozzarella into pieces.
Heat the oil in a pan. Stir-fry the minced meat for 5-6 minutes until crumbly. Season with salt and pepper. Add shallot and harissa and continue frying for about 1 minute. Add 100 ml water, stir in broth.
Bring to the boil and simmer for about 2 minutes until the liquid has almost evaporated. Add beetroot, corn and thyme. Season to taste with salt and pepper.
Remove sweet potatoes from the oven, cut lengthwise, break apart slightly with two spoons. (Leave the oven on.) Lightly loosen the inside of the sweet potatoes with a fork and add 1 tsp. butter to each sweet potato.
Put the sweet potatoes back on the baking tray. Fill with chopped mix and sprinkle with mozzarella. Bake the sweet potatoes in the oven at the same temperature for 5-10 minutes until the mozzarella has melted.
Take the sweet potatoes out of the oven and let's go.