Place the livers in a single layer in an ovenproof dish, and pour over enough Cognac to allow the livers to marinate in it for several hours. Turn them over half way through so both sides absorb the alcohol.
Preheat the oven to 200C/400F/Gas 6.
Add the garlic, basil and salt and freshly ground black pepper to the livers. Gently poach the mixture in the oven for around 5 minutes, turning them over after a couple of minutes. Continue to poach until they are cooked on the outside, but pink within. Do not overcook at this stage, or you will end up with a drab brown crumbly result. Allow to cool slightly.
Tip the contents of the dish straight into your blender with 250g/9oz of softened butter. Whiz until smooth. Check the seasoning, scrape into a terrine and leave to cool.
Clarify the remaining butter by melting it, and straining off the clear liquid, leaving the curd-like sediment. Pour the buttercup-coloured clear liquid over the surface of the terrine, place a couple of fresh basil leaves in the centre, and place in the fridge until set.
Serve with chunks of wholemeal bread and the chutney and salad to the side.