Preheat the oven to 220°C (200°C fan-forced). 

Place the potatoes in a large saucepan of salted cold water and bring to the boil. Cook for 15-20 minutes, until just tender but still holding their shape. 

Place the rosemary, thyme and garlic in a small ovenproof dish, or in the centre of a square of foil. Pour over the olive oil, then fold the foil into a sealed parcel if using. Roast for 15 minutes, until the garlic is lightly golden and the oil is fragrant, then set aside. 

Toast the fennel seeds in a dry frying pan over medium heat for 1-2 minutes, shaking the pan, until fragrant and slightly darker. Tip into a mortar and pestle. 

Add the salt to the fennel seeds and crush until well combined to make a rustic fennel salt. 

Drain the potatoes well and leave them to steam dry for 5 minutes. Give the colander a good shake to rough up the edges, which helps them crisp up when roasting. 

Transfer the potatoes to a large baking tray and sprinkle over the fennel salt. Drizzle with the infused oil, reserving the garlic and herbs, then toss well to coat. Spread the potatoes into a single layer without overlapping. 

Increase the oven to 260°C (240°C fan-forced). Roast the potatoes for 30 minutes, then turn them over and return to the oven for a further 30 minutes, until deep golden and crisp. 

Sprinkle over half the parmesan, add the reserved garlic and herbs, and gently toss to combine. Switch the oven to the grill setting and cook for a further 5-10 minutes, watching closely, until the parmesan is golden and the edges are extra crispy. 

Remove from the oven and serve immediately, topped with the remaining parmesan.