Place the potatoes in a large saucepan. Cover with 3 cm water. Bring to the boil over high heat and cook, covered, for about 25 minutes until just tender, drain. Transfer to a clean tea towel or some kitchen paper to dry.
Brush a large baking tray with oil and spread the potatoes on the tray. Using a potato masher, press down on each one to flatten.
Place the tray in the fridge for 1-2 hours to allow the potatoes to cool completely.
Preheat the oven to 200 degrees C. Drizzle over the remaining oil (use a pastry brush to distribute the oil evenly) and roast for 15 minutes, turning once, until the potatoes are crispy and golden.
Season with salt, scatter with the herbs and serve with steamed asparagus, baked salmon and herb mayonnaise.