25 g (1 oz) butter
2 tablespoons olive oil
1 small onion, finely chopped
1 garlic clove, crushed
2 leeks, cleaned and cut into julienne strips
350 g (12 oz) sole fillets, skinned and cut into thin strips
225 g (8 oz) white crabmeat, flaked
4 tablespoons chicken stock
1 small avocado, peeled, halved, stoned and sliced
1 teaspoon grated lemon rind
salt
1 teaspoon green peppercorns in brine, drained
2 tablespoons finely chopped fresh parsley or dill, to garnish