Butterfly the chicken breasts and brush with a little olive oil, season well and griddle on either side for 3 minutes.
For the gravy
Add the chicken stock and wine to a pan and bring vigorously to the boil. Remove from the heat and add the cornflower, add a pinch of sugar and season with salt and pepper to taste, stirring well until all is dissolved.
For the vegetables
Fry off the onion in a little oil for a couple of minutes until softened.
Blanch the asparagus and peas in boiling water for 4 minutes. In separate pan melt the butter until foaming. Add the asparagus and peas, chopped sage, seasoning and softened onion. Toss together in the pan for about 2 minutes.
Melt the goose fat in a pan until it is really hot. Take the pre-cooked new potatoes and fry them until they are crispy on all sides.