Divide the cauliflower into florets and cook in salted boiling water until firm to the bite. Cut the spring onions into rings.
Heat the oil in a pan and fry the minced meat in it over medium heat until crumbly. Salt, pepper and fry the spring onions briefly. Add tomato paste and broth, season with cayenne pepper and simmer for 2 - 3 minutes over low heat.
Grease a refractory dish. Layer the minced meat and cauliflower alternately. Finish with cauliflower.
Preheat the oven to 220 ° C top / bottom heat (convection 200 ° C, gas: level 4).
Cut the cheese into wide strips and place them in a grid over the cauliflower. Bake the gratin in the hot oven for about 15 minutes until the cheese has melted.
Tip: if you want to freeze the casserole, leave out the cheese. Put this on top before gratinating.