Smash the garlic cloves and peel off the skin. Place the cloves onto a baking sheet and drizzle with ~1 tbsp avocado oil and mix so that the cloves are coated in oil. Place the baking sheet in the oven set to 450 F.
While the garlic is roasting, slice the potatoes. Hold one end of a potato firmly and using a sharp knife, carefully make slices about 1-2 mm apart widthwise across the potato. Cut down 2/3rds of the way, not all the way through the potato!
Once you’ve sliced the potatoes, peel the onion and cut it into slices.
Add the potatoes (sliced side up) and the onion slices to the baking sheet and mix them around so that they are coated in oil. Drizzle each potato with a little more avocado oil, and then sprinkle on the rosemary and a generous amount of sea salt and pepper.
Return the baking sheet to the oven. Roast for about 30 minutes. Check the potatoes and add more oil to the potatoes if they look like they need it! Mix around the onions and garlic and remove them if they look like they are burning!
Roast in the oven for another 30 minutes, or until the potatoes are soft on the inside and crispy on the outside!
Enjoy the potatoes with a side salad dressed in a simple balsamic vinegar dressing!