Put 1 cup (250 ml/8 fl oz) water in the lower compartment of a microwave steamer.
Cover and microwave on HIGH for 3 minutes.
Rinse and drain the cabbage and put into the perforated compartment of the steamer and place above the boiling water.
Cover and microwave on HIGH for 10 minutes.
Rinse the fish under plenty of cold running water and pat dry on kitchen paper.
Cut the fillets in half lengthwise.
Salt both sides.
Crumble half the thyme over.
Mix together the vinegar, cognac and remaining thyme.
Sprinkle salt and pepper over the base of a square shallow casserole.
Spread the shredded cabbage over the base of the casserole.
Pour the vinegar and cognac mixture over and add salt and pepper to taste.
Using half the butter, dot tiny pieces on top.
Arrange the fish fillets on top.
Dot with the remaining butter.
Cover and microwave on HIGH for 5 minutes.
When the fish is cooked, adjust seasoning and pour the lime juice over.