Fill a large pot with water and bring to a rolling boil. Add 1 tablespoon of salt to the water. Add the potatoes and boil for 20–25 minutes (small) or 30 minutes (medium) until a knife slides in with zero resistance.

Preheat your oven to 200°C / 390°F (180°C fan-forced). Make sure it reaches full temperature before the potatoes go in.

Drain the potatoes into a colander. Leave them uncovered for 5 minutes to steam dry. Do not cover them — this lets surface moisture escape naturally.

Transfer the potatoes to a large baking tray, spacing them apart so they don’t touch. Using a potato masher, large fork, or flat-bottomed glass, press down firmly on each potato to flatten it. Don’t worry about making them look neat — a rough, uneven surface creates more crispy edges.

Leave the smashed potatoes on the tray for another 5 minutes to steam dry a second time. This second drying round is key to maximum crispiness.

Drizzle the melted butter over all the potatoes, then drizzle the olive oil on top. Scatter over ¾ tsp salt and ¼ tsp black pepper. Make sure every potato is well coated.

Bake in the preheated oven for 45 minutes (small potatoes) or 55 minutes (medium potatoes). Do not flip them at any point. Bake until deeply golden-brown all over. If your oven runs cool, add 5–10 extra minutes.

Remove from the oven and scatter with freshly chopped parsley if using. Serve immediately for maximum crunch.