Preheat the oven to 220°C.
Season the plaice fillets and roll them up.
Slice one lemongrass stalk into four skewers and pierce each roll to secure.
Butter a small ovenproof dish and add the chopped shallots and crushed garlic.
Blanch tomatoes for one minute, peel them, and reserve the skins and seeds.
Place the tomato skins and seeds into the dish and dice the tomato flesh into small cubes.
Brown the fish rolls in half of the butter for one minute per side in a hot pan.
Transfer fish to the oven dish and pour over 110ml white wine and 175ml fish stock.
Cover with foil and bake for 7-10 minutes until the fish is cooked.
Sieve the cooking liquid into a pan and simmer until reduced by half.
Stir in tomato cubes, cream, tarragon, and the remaining lemongrass to warm through.
Wilt the baby spinach in a separate pan with the remaining butter.
Plate the spinach, top with fish rolls, and spoon the sauce over.