Parboil the potatoes in a large saucepan of boiling, salted water for 15 minutes. Drain and leave to cool for a few minutes to one side.
Preheat the oven to 180°C.
Place the salmon in a ceramic baking dish and rub with some of the olive oil. Rub in the garlic as well, then sprinkle over the sliced pancetta. Add the potatoes, cutting any that are much larger, and season well with salt and pepper.
Sprinkle over the thyme leaves and pour in the rest of the olive oil. Bake for 20 minutes. Remove after 20 minutes and leave to stand for a few minutes before garnishing with a sprig of thyme and a little more seasoning.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.