Preheat the oven to 190 C, 170 Fan, Gas 5. Prick the sausages all over and brown them quickly in half the butter. Transfer to an ovenproof dish that is just large enough to take them in a single layer.
Reduce the heat under the pan, add the remaining butter and fry the onion and garlic gently until tender and translucent. Add to the sausages.
Drain any fat from the pan then return to the heat. Pour in the red wine and bring up to the boil. Stir in the redcurrant jelly then pour over the sausages.
Tuck in the bouquet garni and season with salt and pepper. Cover with foil and bake for about 30 minutes. Serve immediately with piles of fluffy mash