1. Vac-pack the watermelon and put it in the fridge for 3 days.
2. Preheat the oven to 200c
3. To make the sauce, pour the madeira into a saucepan and bring to the boil. Then, add the demi glace, reduce by half and finish with the butter  and sauteed mushrooms.
4. Meanwhile, pan fry the brioche in a little butter and put to one side. In the same pan, drizzle in the oil, season the steaks, then fry for 2 minutes. Turn over, add the butter and cook for a further 2 minutes. Pop in the oven for 5 minutes, then rest.
5. Wilt the spinach in another pan with the butter, season, and then drain.
6. Pan fry the watermelon in butter on both sides for 1 minute.

To serve, put the brioche into the centre of the plate, top with the watermelon, spinach, then the steak, and finally, spoon over the sauce.