Preheat the oven to 200 degrees
Place the potatoes one at a time on a tablespoon and slice along the whole length.
Put the potatoes in an ovenproof dish and drizzle with rapeseed oil (or a cooking oil of your choice) and sprinkle over the grated garlic. Bake for 30-40 minutes.
When cooked transfer the potatoes to a large bowl and add the chopped tarragon, lemon zest and seasonings. Stir well and allow to stand for a few minutes before serving.