If your potatoes have dirt on them, wash and scrub your potatoes.
Place them in a large pot of well salted water over a medium high heat and cook for 20-30 minutes or until the largest potato can easily be pierced with a knife.
While you wait, preheat the oven to 200C/400F. Move your racks to have space for two oven trays if necessary. Get two oven trays out and measure the butter for the sauce into a small pot.
Crush your garlic and pick any woody stems off the sage.
Once the potatoes are cooked, drain them. Place half of the cooked potatoes on each tray then drizzle over half the oil and season with salt per tray. If the potatoes are cool enough, use your hands to massage the oil and seasoning into each potato.
Space the potatoes out evenly on each tray. Use a large flat-bottomed mug (I like to use a pouring jug) to gently put pressure on the first potato, squishing it down. Try to go slowly but firmly so that you don’t completely break the potato apart – we want it flattened but held together by the potato skin. Repeat with the remaining potatoes.
Place the trays in the oven for 25 minutes, then swap them over so that each tray gets equal browning. Cook for an additional 20-25 minutes.