Preheat the oven to 425°F (220°C). Oil a baking sheet large enough to accommodate your plaice. Season the surface of the baking sheet and place the fish on it, pale side (underside) down. Drizzle the fish with olive oil and massage it in. Season all over with pepper and lots of salt and dot the little pieces of butter over it.
Scatter the cherry tomatoes around the fish, along with the thyme and bay leaves. Bake for 20 to 30 minutes, until the fish is just cooked and the tomatoes are blistered and soft.
Once roasted, the flesh of the plaice should lift easily from the bone in neat fillets. Remove the top two fillets using a fish knife and fork. Ease the skeleton away to reveal the remaining two fillets from the underside. Serve the fish with the tomatoes and all the buttery, salty-sweet roasting juices.