For the venison, preheat the oven to 200C/400F/Gas 6.
Heat the oil in a frying pan, add the venison and colour it well all over. Season with salt and pepper.
Transfer the venison to a roasting tray and roast for five minutes.
Turn down the oven to 180C/350F/Gas 4. Add the butter and sage leaves to the meat and roast for a further 8-10 minutes, basting frequently. When cooked, remove from the oven, season if necessary, and leave to rest in a warm place.
For the endive, turn down the oven to 160C/325F/Gas 3.
Bring a pan of salted water to the boil. Blanch the endives, then drain and transfer to an ovenproof dish. Pour the stock around them and dot with the butter. Bake for 30 minutes, or until cooked, but without colour.
Remove the endives from the oven. Once they are cool enough to handle, gently squeeze them to remove any excess liquid and cut them in half lengthways.
Using the same pan you used to brown the venison, heat two tablespoons of oil over a high heat. Add the endives cut-side down for 2-3 minutes, or until caramelised. Transfer to a plate and keep warm.
For the sauce, heat the oil in a saucepan, add the trimmings and cook to colour them all over.
Add the vegetables and sage stalks and cook to colour them, then add the wine and stock and cook until the volume of liquid is reduced by half.
Strain the sauce through a sieve into the pan you caramelized the endives in, then beat in the butter. Taste and adjust seasoning as necessary.
To serve, carve the racks of venison and serve with the endives. Garnish the endives with chives and pour the sauce around.