Preheat your oven to 220°C/200°C(fan)/430°F/Gas 7.
Melt 100 g Butter and add 3 Garlic clove, 2 g Fresh rosemary, 5 g Fresh parsley and 1 pinch Sea salt and black pepper. Mix well and set aside.
Using a thin, sharp knife, make slices three quarters of the way through each of the 800 g Potato. Try to get them as close together as possible (about 2-3mm) and make sure you don't cut all the way through.
Put the potatoes in a baking dish and season. Slowly pour over the herb butter mix, making sure it goes into as many of the slices as possible.
Put in oven for 60 minutes (depending on the size of the potatoes).
Notes
You can make mini versions of this by using baby potatoes.
If you don't love rosemary, then you can swap it for fresh thyme.
You can make sweet potato hasselback potatoes, but they won't get quite as crispy.
You need to make sure you are putting these in a very hot oven. This helps to get them really crispy.
If you want to make these hasselback potatoes a little more indulgent, then 10 minutes before the potatoes have finished cooking, add some slices of mature cheese in between the slices of potato.